The Objective Assessment of Striking Force in Combat Sports Using Sport-Specific Measurement Devices – – a Review

 ORIGINAL ARTICLE

The objective assessment of striking force in combat sports using sport-specific measurement devices – – a review

Authors’ Contribution: Anna Akbaş1ABD, Anna Brachman1ABD, Bartłomiej Gzik2BD, Bogdan Bacik1AD A Study Design B Data Collection 1 Institute of Sport Sciences, Academy of Physical Education, Katowice, Poland C Statistical Analysis 2 D Manuscript Preparation Students Scientific Circle ‘Biokreatywni’, Faculty of Biomedical Engineering, Silesian University of Technology, Zabrze, E Funds Collection Poland

Received: 14 June 2020; Accepted: 28 June 2021; Published online: 30 June 2021

AoBID: 14548

Abstract

Background and Study Aim: Throughout the literature, numerous measurement systems have been designed aiming to provide a point of reference to scale the intrinsic performance of combat sports athletes. However, magnitude of force exerted by the athletes varied greatly between studies and it is difficult to find consistencies in research in this area. Thus, the purpose of this study was to review recent research regarding the striking (punching and kicking) forces and usefulness of sport-specific measurement devices exclusively dedicated for combat sports athletes. Material and Methods: The search of following databases: SPORTDiscus, Scopus, Google Scholar, PubMed and Springer were conducted using different combination of terms: (training simulator OR training device OR device) AND (combat sports OR martial arts OR judo OR karate OR taekwondo OR boxing OR mixed martial arts OR Thai chi).

Results: The literature search retrieved a total of 4028 and 9 of them met inclusion criteria. The target-based measurement devices: punching bags, manikins and impact platform, as well as wireless in-glove systems were used. Most of the included studies showed significant influence of gender, level of expertise and the striking technique on the impact forces associated with punching and kicking.

Conclusions: There are plenty of valid, accurate and reliable devices which opens up new possibilities in enhancing combat sport training and performance. Unfortunately, because of the large methodological and technological diversity, the results obtained by different studies cannot be directly compared. The future research perspectives should include the evaluation of diverse groups of athletes across different force measurement devices.

Key words: boxing manikin • force sensors • impact force • kicking • martial arts • punching • punching bag • strain gauge Copyright: © 2021, the Authors. Published by Archives of Budo Conflict of interest: Authors have declared that no competing interest exists Ethical approval: The study was approved by the local ethics committee Provenance & peer review: Not commissioned; externally peer-reviewed

Source of support: Departmental sources Author’s address: Anna Akbaş, Institute of Sport Sciences, Department of Human Motor Behaviour, Academy of Physical Education in Katowice, 72a Mikołowska Str., 40-065 Katowice, Poland; e-mail: [email protected]

This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (http://creativecommons.org/licenses/by-nc/4.0), which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non-commercial and is otherwise in compliance with the license. Original Article

INTRODUCTION Straight punch – is also Considering all the above, the purpose of this known as „cross”, because dur- One of the fundamental aim in sport is to maxi- study was to review recent research regarding punch the blow crosses over the leading arm. This is mize athletes’ performance. Research and innova- ing the striking (punching and kicking) forces a punch thrown with the dom- tion technology provide an increasing number of and usefulness of sport-specific measurement inant hand the instant an opponent leads with his oppo- information about motor characteristics, technique, devices exclusively dedicated for combat sports site hand. tactics and psychological features of the athletes, athletes.

Hook punch – typical box- supporting thereby physical training [1, 2]. ing punch, performed by turn- ing the core muscles and In the combat sports, such as boxing, karate, tae- back, thereby swinging the MATERIAL AND METHODS arm, which is bent at an an- kwondo, etc., results are determined by a number gle near or at 90 degrees, in Search strategy a horizontal arc into the oppo- of interrelated factors like strength, coordina- nent. A hook is usually aimed tion, speed and stamina [3-6]. Among various Publications search was time restricted from at the jaw. components the striking force is considered year 2000 to 2021. The search of following data- Front kick – in martial arts is a major determinant of a fighter’s victory [7-11]. bases: SPORTDiscus, Scopus, Google Scholar, a kick executed by lifting the Generally, striking aims to impose physical dam- PubMed and Springer were conducted using knee straight forward, while keeping the foot and shin ei- age, develop tactical advantage, and score points different combination of terms: (training simu- ther hanging freely or pulled to against an opponent [4, 9]. lator OR training device OR device) AND (com- the hip, and then straighten- ing the leg in front of the prac- bat sports OR martial arts OR judo OR karate titioner and striking the tar- Several authors have highlighted that the strik- OR taekwondo OR boxing OR mixed martial get area. ing forces can be measured and analysed to arts OR Thai chi). Furthermore, manual searches Apdolio – is a typical tae- provide diagnostic, programming and prognos- based on the references listed in the reviewed kwondo kick. Also known as tic information for talent identification or team articles were performed to complete the search. „fast kick”. During punch feet goes for 45’ down, knee is selection [4, 12, 11, 13]. Changes in striking Literature search was completed in March, 2021. raised higher than feet, then force, as one of the key indicators of perfor- Early screening of the articles based on the titles leg straightens. mance [7, 14, 15], may enhance designing of and abstracts was performed by two authors BG Dwit Chagi – is a typical tae- accurate strength and conditioning interven- and AB. Full-text articles were independently kwondo kick. From the stand- ing position, one lifts up the tions [16, 17, 15]. Furthermore, the measure- assessed by authors AA and BB. kicking leg and stretches it ment and analysis of striking forces can serve as backward to deliver a kick. The back is sole is used for an indicator for categorizing combat sport ath- Eligibility criteria the kick. letes according to their punching forces [11, 4]. Studies were chosen under following inclusion criteria: (1) full-text was available in English, Yop Chagi – is a typical taekwondo kick. One lifts up the Throughout the literature, numerous measure- (2) the publication was an full-length origi- kicking leg, folding the knee, ment systems have been designed aiming to pro- nal research, (3) at least one group of subjects and then stretches the fold- ed knee as he or she turns the vide a point of reference to scale the intrinsic were healthy combat sports or martial arts’ ath- body in the opposite direction performance of combat sports athletes. However, letes, (4) the study included device dedicated to to the target and kick the target with the back sole of foot. magnitude of force exerted by the athletes var- measure strike force in combat sports, (5) arti- ied greatly between studies and it is difficult to cles were included, even if there was no control Bandal Chagui – is a typi- find consistencies in research in this area [16, 18, group. Studies were excluded if they (1) did not cal taekwondo kick. The fore sole or the foot back delivers 8, 14, 1, 5]. Several authors have raised the issue contain human participants, (2) training devices a kick by making a slant circle of discrepancy in reported values of observed were based on virtual reality technology, (3) the of movement. variables [14, 15, 5]. In the literature there are study type was a systematic review, meta‐anal- Impact force – when one several reviews concerning striking force in com- ysis or other non-empirical article. thing is going to hit another one, the impact force interacts bat sports [19, 11, 13]. In most recent review [13], on them. authors highlighted that striking actions must be Measures evaluated in the context of a particular combat Three reviewers (AA, AB and BG) extracted the Calibration - is the method by which the voltage obtained in system. They reported, that the measurement following information independently from the the tensor amplifier, which is of upper limb strikes lacks unification in terms included studies: (1) characteristics of the partic- connected to the sensor, re- lates to the force that is acting of the methodology and equipment used. They ipants (including age, body mass and height, sport on the sensor, expressed in ki- also concluded that most of the reviewed studies discipline, sports level and training experience), los force or in Newtons. were using their measures without justification of (2) characteristics of the devices (conceptualiza- Piezoelectric sensor – is a de- evaluated parameters (indicators). Although this tion, design and construction), (3) characteristics vice that uses the piezoelectric effect to measure changes review contributed to systematizing the state of of the studies. Data were collected and organized in pressure, acceleration, tem- the art in this area, it analysed only upper limb in Tables 1, 2 and 3 . Due to the heterogeneity of perature, strain, or force by converting them to an electri- strike actions and it lacks detail analysis and variables, populations, and design the systematic cal charge. description of the measurement equipment. review and meta‐analysis of data were not feasible.

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RESULTS to simulate head and upper body of a boxer. The Strain gauge – is a device Data synthesis used to measure strain on four tri-axial piezoelectric 9366AB force transduc- an object. The most com- Computerized literature search included five ers were mounted between front and back frame mon type of strain gauge con- sists of an insulating flexible databases and contained a total number of 4028 aluminium frame, where the manikin was perma- backing which supports articles. After title selection and the removal of nently mounted. The force signals were passed to a metallic foil pattern. duplicates, abstracts of 299 original research amplifier and then to analog-to-digital converter to MMA – mixed martial arts papers were reviewed for eligibility. Full text of enable to computer to process dynamometric data. (Piepiora and Witkowski [27] 22 articles was evaluated in detail. Finally, 9 arti- However, in the studies of [14, 10] the boxing man- call MMM practitioners neo- gladiators, because this for- cles met inclusion criteria (Figure 1). ikin had more human-like shape and was dedicated mula of hand-to-hand fighting to evaluate kicking performance. The base of mani- does not meet the formal criteria of sport within the mean- Participants kin was filled with water to maintain its stability. The ing of the Olympic Charter). The total sample size in reviewed articles was 160 model was made from heavy dense foam and was participants (111 male, 49 female) from which equipped with a force platform inside of a torso. Częstochowa declaration 2015: HMA against MMA – majority (95) were athletes of different level of The force platform was constructed of two wooden “continuous improvement of performance. The most commonly assessed ath- plated of 25 diameter each, which included 5 piezo- health through martial arts as one of the most attractive letes were boxers and taekwondo athletes, and resistive pressure sensors in pentagonal structure. form of physical activity for each group was exclusively selected for five out The height of Smith’s manikin was adjustable to the a human, accessible during en- tire life should constantly ex- of ten studies. The detailed characteristic of par- anthropometric features of the trainees, while the ist in public space, especially ticipants was presented in Table 1. Falco’s manikin was adjustable to 3 heights of 160, in electronic media, to bal- ance permanent degradation 173 and 188 cm. of mental and social health by Concept, construction and design of devices enhancing the promotion of mixed martial arts – contem- Manikins Punching bags porary, bloody gladiatorship, The boxing manikins were specially equipped In order to evaluate the punching and kicking per- significant tool of education to aggression in a macro scale”. human shaped models used to simulate the human formance [1] utilized a long cylinder-shaped bag body during a single or a series of punches/kicks. In (L = 1.8 m, D = 0.42, mass = 41 kg) with a shock Gdansk 2nd HMA World Congress Resolution – the study of [16] the boxing manikin was designed absorbing outer layer, equipped with two 3D Article 1 The white flag with five interlocking “Olympic rings” is the most recogniz- able symbol in the global public space. Neither did the res- urrected idea of Olympia, “Citius, Altius, Fortius” save humanity from the hor- rors of two world wars, nor did the declared mission of the International Olympic Committee (IOC): “1. (…) the promotion of ethics and (…) ensuring that, in sport, the spirit of fair play prevails and violence is banned” (Olympic Charter, p. 18) stop the pa- thology of permanently edu- cating contemporary man in aggression. Article 2 Likewise, symbols (a sword point- ed downwards surround- ed by five rings) and motto (“Friendship through Sport”) of Conseil International du Sport Militaire (CISM) did not stop soldiers from killing each other and murdering people after 1948 (the year of estab- lishing CISM, the second larg- est multi-sport discipline organization after the IOC, and also the year of the Universal Declaration of Human Rights). Article 3 Although there are five identical combat sports in the Olympic Games and the Military World Games, their potential is still not used to meet the second of the Fundamental Principles of Olympism: “(…) to place sport at the service of the harmoni- Figure 1. The flowchart for the literature search process. ous development of human-

kind, with a view to promoting Table 1. Basic characteristics of the participants in included studies. a peaceful society concerned with the preservation of human dignity” (Olympic Charter, Combat Sex p. 13). Article 4 Boxing and Source sport Age Weight [kg] Height [m] Level of Experience wrestling cultivate the tradi- (martial [years] competition [years] tions of ancient Olympism. arts) M F Judo and taekwondo have giv- en martial arts humanistic and health attractiveness. Fencing 7 0 23.1 69.9 1.78 ±0.06 elite 11.5 combines this tradition with ±1.2 ±8.6 ±1.4 modernity in the spirit of chiv- alry. Aiming dynamic offensive Smith M et al. 23.5 73.4 5.7 and defensive actions direct- (2000) [16] boxing 8 0 ±3.3 ±8.2 1.75 ±0.05 intermediate ±1.3 ly at the opponent’s body (ir- respective of the protectors 23.6 78.5 1.5 used) in such a way as not to 8 0 1.79 ±0.02 novice hurt is a measure of respect- ±3.2 ±8.9 ±0.2 ing those knightly rules. This rule harmonizes with the prin- Pierce J et al. boxing 12 0 27 78.95 - legendary - ciple of respect for the oppo- (2006) [8] ±9 ±19.95 blue horizon nent’s as well as one’s own corporeality and dignity over the vain victory at all costs. 15 0 expert Falco C et al. Article 5 For the civilized in- taekwondo 21.57 ±4.75 - - at least 4 dividual and the society for (2009) [14] whom human health and dig- 16 0 novice nity are the common good, participation, in any role, in brutal shows of people mas- 13 0 medallists sacring each other cannot be Estevan I et al. 72.04 a standard of the quality of (2011) [10] taekwondo 26.56 ±2.23 ±12.67 1.77 ±0.86 at least 4 life. Neo gladiatorship cam- non ouflaged under the banner of 14 0 medallists martial arts or combat sports is a slight to the Fundamental 17.0 1.7 3.1 Principles of Olympism, boxing 13 7 ±1.1 68.9 ±12.4 ±0.1 - ±1.6 but also to the Universal Buśko L et al. Declaration of Human Rights. (2016) [1] Therefore, this Resolution taekwondo 14 14 18.7 62.9 1.75 ±0.13 - 8.1 should inspire as many ac- ±3.1 ±8.1 ±2.8 tors of Knowledge Society as possible jointly to oppose Šiška L et al. boxing 4 8 20.6 67.6 1.708 Boxing club 2.6 any deformations of the mis- (2016) [20] ±4.4 ±10 ±0.084 Ruzinov 821 ±1.6 sion of Olympism and sport. The expansion of the pathol- ogy of unauthorized nam- kung fu 2 0 ing neo gladiators as combat sports athletes will soon turn the Fundamental Principles of karate 6 2 Olympism into their own car- icature – objective indicators are a testament to the dev- taekwondo 3 0 Australian astation of all dimensions of 31.6 Defence health by the practice of legal 86.2 ±20.5 - - bloody pageants [28]. Ramakrishnan K et al. ±10.3 Force (2017) [21] Muay Thai 3 0 Academy

MMA* 1 0

judo 1 0

28.1 untrained 26 8 ±7.2 77.4 ±17.4 - - - World Buśko K and Nikolaidis taekwondo 6 0 17.7 62.3 1.795 Taekwondo 6.5 P.T. (2018) [15] ±0.7 ±6.0 ±0.041 Federation ±1.6 Jovanovski A and Stappenbel A boxing 21 10 - 72.7 ±11.7 1.74 ±0.07 novice - (2020) [5]

* MMA (see glossary)

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accelerometers located on the edge surface of of the foam padding of the gloves. In this study the punching bag’s inner cylinder base. The ded- the authors used capacitive force sensors which icated software enabled the calculation of strike were originally designed and patented for isomet- forces in three directions based on the mass of the ric knee muscle torque measurements [22]. Both punching bag and the sum of acceleration of upper systems were designed to obtain maximal force and lower edge of the punching bag. The calcu- of impact and caused no discomfort to the ath- lation of the point in which the strike was deliv- letes during punching assessment. ered was calculated taking into account moments of inertia against the punching bag’s centre of Other devices mass, upper and lower edge acceleration, distance In the study of [21] the ‘Kick test rig’ was between these two points and the force of strike. designed to measure kick force and displace- The accelerometer-based approach has been also ment of the target (Table 2). The target was com- used by [20]. The subjects were asked to deliver posed of the vertical plate of a contact area of a punch into the FiTRO agility plate mounted on 400 mm x 275 mm made from aluminium, indus- athletes’ eye level. The single accelerometer was trial strength vinyl and padded with high-density placed on the opposite side of the punching bag foam in order to prevent injuries. The target was (L = 1.9 m, mass = 50kg) approximately at the fixed on steel beam which served as a carriage height of the centre of the plate. The calculation moving in horizontal axis. The force was mea- of the punch force was based on the mathemati- sured by a S-type Dacell load cell with a capacity cal formula, where force is a product of punching of 1000 N, while the displacement of the target bag’s mass and acceleration. was obtained by a linear variable displacement transducer attached to the target. In contrast, in the study of [15] relatively small (L = 0.5 m, D = 0.48 m) punching bag suspended Calibration on a set of stabilizing ropes with in-built strain Most likely, the calibration of punching bags and gauge was used. The system was appropriate force plates involved the pendulum-like unit of to measure the resultant reaction force in the a known weight which was striking against mea- plane perpendicular to the cylindrical surface of surement device. In the study of [16] the pendu- the punching bag. The punching bag was exter- lum impactor was a steel ball in the shape of a fist nally connected with the strain gauge amplifier covered by a boxing glove (Top Ten, Germany) equipped with the analogue-to-digital converter. which hit the dynamometer manikin at an angle of 90º with a mass of 4.4, 20, 45 and 60 kg. Four All of the punching bags were equipped with impacts at each calibration mass were filmed what diodes which played a role of visual signal to allowed a comparison between recorded and cal- start the punch [20] or were guiding the strike culated impact forces. The force measurement sequences [1, 15]. error was less than 3%. In the study of [1], the dynamometric impact hammer equipped with In-glove systems a strain gauge-based force transducer was sus- The in-glove systems were introduced in the pended and pulled back away from punching studies of [8, 5]. The systems enabled evalua- bag in order to deliver 5 to 8 strikes to punching tion of the boxers technique and punching phys- bag. The transducer was connected to light metal ics during matches within the boxing ring. It also spherical cap through which strike force was trans- addressed the problem of overestimating the ferred onto the dynamometric punching bag. The actual force delivered by boxer while punching an values of impact forces obtained by strain gauge inanimate object in comparison to punching the were compared to the values of force obtained moving opponent. The systems took into account and calculated from accelerometers embedded the multidirectional components of punch, as to the punching bag. The measurement error of well as dynamic and repeated nature of boxing. In force was less than 1%. In the study of [21] the the study of [5] the non-embedded in-glove sen- ‘kick test rig’ was calibrated using 40 kg steel cyl- sors consisting of 3D accelerometers and piezo- inder suspended on a steel cable. The measured resistive force sensors were used. The sensors energy was compared with the energy applied to were 1-ich and covered the impact area on the the platform during impact showing that 98% of fist. Similarly, in the study of [8] the lightweight, energy from the pendulum was transferred. These flexible force sensors were adjusted to the hit- results implied, that only small amount of energy ting area (120 cm2 ), however were located inside was lost in friction and inertia.

Table 2. Technical characteristics of devices dedicated to measure force of striking in included studies.

Table 2. Technical characteristics of devicesConstruction dedicated to measure of training force of striking simulator in included studies. Combat sport Additional devices used Source Combat (martial arts) Construction of training simulator in the study sport Schematic representation/ Additional devices used in SourceType Device design Software (martial PhotographSchematic representation/ the study arts) Type Device design Software

Photograph

Four triaxial piezoelectric 9366AB force transducers A 16-mm Photosonics 500 A 16-mm Photosonics 500 Four triaxial piezoelectric cine film camera (Thame, (Kistler, Alton, UK), boxing cine film camera (Thame, 9366AB force transducers UK), fitted with a SigmaUK), fitted with a Sigma manikin(Kistler, designed Alton, UK),to boxing Provec 5 0.024-m lens (Whitbys, Boxing manikin designed to simulate Provec 5 0.024-m lens (Whitbys, Smith M et al. SmithBoxing M et simulate the head and clinical Chichester, UK), NAC DF- al. (2000) boxing dynamome the head and upper body of the boxing data clinical16C projectordata Chichester, UK), NAC DF-16C (2000) [16] [16] dynamometer ter upper oxer,body 9851 of thecharge oxer, amplifier software (International IML, Thame, system (Kistler, Alton, UK), software projector (International IML, UK), Terminal Display 9851 charge12-bit PC26AT amplifier analog -to- System TP1067 digitizingThame, UK), Terminal Display digital converter system (Kistler, Alton, UK), tablet (Bracknell, UK) 12-bit PC26AT analog-to- System TP1067 digitizing digital converter tablet (Bracknell, UK)

Boxing gloves (modified Everlast 1008 8-ounce and Best Shot System 1010 10-ounce Pro-Fight) TM incorporating the best Pierce J et al. boxing by Sensorpad shot System (lightweight, - - (2006) [8] Systems, Inc. flexible force sensor (SPS; Norristown) embedded in the scoring section of the glove), remote receiver, PC

Freestanding boxing mannequin, a force platform, made with two Falco C et al. A201 moby circular wooden plates Visual Basic (2009) [14] taekwondo FLEXIFORCE of 25cm diameter, five 6.0 HP computer, microcontroller Company piezoresistant pressure sensors in a pentagonal structure on the mannequin

Freestanding boxing mannequin, a force platform, made with two Estevan I et al. A201 moby circular wooden plates Visual Basic (2011) [10] taekwondo FLEXIFORCE of 25cm diameter, five 6.0 HP computer, microcontroller Company piezoresistant pressure sensors in a pentagonal structure on the mannequin

boxing Dynamometric punching bag (1.8 length, 0.42 diameter, 41 kg mass, stiff Special dynamometric Boxingboxing Training core, shock absorbing outer impact hammer equipped Buśko L et al. Dynamometric punching bag BTS6v0 with a strain gauge-based Simulator (BTS- layer)(1.8 with length an, 0.42embedded diameter, 41 Special dynamometric Boxing (2016) [1] kg mass, stiff core, shock softwareimpact hammer forceequipped transducer equipped 4AP-2K) Trainingtwo tri-axial accelerometers Buśko L et absorbing outer layer) with an BTS6v0 with a strain gauge-based al. (2016) Simulator with a light metal spherical mountedembedded on the two edgetri-axial software force transducer equipped [1] (BTS- cap accelerometers mounted on the with a light metal spherical taekwondo 4AP-2K)surfaces of the punching Taekwondo edge surfaces of the punching cap bag’sbag’s inner inner cylinder cylinder base base

the punching bag with attached accelerometer, the punching bag with attached FITROaccelerometer, agility plate, FITRO light agility Šiška L et al. Šiška L et BOX- plate, light emitting diode boxing al. (2016)BOX-CHECK boxing emitting diode which - - - - (2016) [20] [20] CHECK which present visual stimuli present(red visuallamp) connected stimuli (redto the PC lamp)with connected dedicated software to the PC with dedicated software

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Construction of training simulator Source Combat sport Additional devices used (martial arts) Schematic representation/ in the study Type Device design Photograph Software

Vertical plate with a contact area of 400 x 275 mm, rectangular hollow section Ramakrishnan K martial arts Kick Test Rig steel beam, twin-airbag - Casio Ex-F1 camera et al.(2017) [21] system, S-type Dacell load cell, linear variable displacement transducer

Dynamometric punching bag (0.5 m length, 0.48 m diameter) with an embedded strain gauge, BTS5v0 (1) Kistler force plate Type 2 signal diodes on an specialist 9281A Buśko K. and Boxing Training upper section of the bag, software (2) special torque meter type Nikolaidis PT taekwondo Simulator (BTS-3) strain gauge amplifier, („JBA” Zb. SMS1 and SMS2 (2018) [15] signal conditioning sub- Staniak, (3) Monark 874 E cycle assemblies, analog Poland) ergometer converter; connected with PC by USB interface; hanged on stabilization rope

Embedded Jovanovski A and in-glove In glove sensors: tri-axial The Bluehill Stappenbelt boxing measurement accelerometer and piezo- - Software static measurement system A (2020) [5] system resistive force sensor

Different approach has been used to calibrate Measuring outcomes force sensors located in the boxing glove or box- The values of the impact forces associated with ing manikin. In the study of [5] the piezo-resis- striking depend on several factors, such as the tive force sensors were calibrated by punching limb involved (lead or rear), type of the task, gender, a static measurement system utilizing simple load experience, athlete’s body weight and environment cells for force and laser displacement for glove in which the assessment has been done (Table 3). speed measurements. The static measurement system generated a calibration coefficient applied The influence of task: punching to the voltage output of the force sensor in order The type of the punch did not show signifi- to provide the value of force in N. Similarly, in cant differences in the impact forces in elite tae- the study of [14] calibration allowed to relate the kwondo practitioners (straight punch 1659 N voltage output (obtained in the tensor amplifier) ± 254.2 vs. hook punch 1843.8 N ± 453.3) [15]. to the force acting on the sensor (expressed in N). The rear hand punching reached higher values of It was realized by linear interpolation and placing impact forces than lead hand in elite male boxers: 2 kg by 2 kg until reaching 20 kg, and 10 kg by 10 1592.5 N ±507.1 vs. 1102.9 N ±430.7 [1], kg until reaching 110 kg in total. 4800 N vs. 2847 N [16], female elite boxers: 1170.7 N ±165.3 vs. 848.4 N ±218.5 [1], interme- At last, in [8], the drop platform apparatus was diate boxers: 3722 vs. 2283 N, and novice box- repeatedly lifted and dropped on the boxing glove ers: 2381 vs. 1604 N [16]. Higher impact forces from various heights. These created impacts of generated with rear limb were associated with known forces measured by the load cell attached significantly higher maximal joint torques in flex- to the centre of the platform. The average error ors and extensors of elbow joint in the same limb of force was 4%. (54.2 Nm ±8.5 vs 61.7 Nm ±12.7) [15]. Additionally,

Table 3. Summary of included studies. Conclusion discriminated dynamometer boxing The punching performance between effectively at of performance the 3 standards and between and lead hands. of the rear punching force punch force measure is able to system The It brings benefits match. during boxing judging (punch effectiveness), training for of punch), and monitoring measure (objective (safety benefits). boxers powerful in longer distances more Expert were Distance in all distances. than novice and faster as on impact an influence force did not have increases. level competition observed in impactwere time in differences No groups. between distances of the execution any hitting with less execution Medallists were than non- max impact force time and greater medallists. functional is sufficiently to be used system The the same while at diagnostics in taekwondo for diagnostic capabilities greater time offering boxing. for be used during whole may „Box-check” Device 50-100 punches for session i.e. training rear and hook of front, combination different punches with body increasing was energy kick The was however of participant and gender, weight not with martial 1 in 100 adults arts training. exceeding with energies kick will be able to 215 J. the punching that show to likely are results The depend on other factors, may force and kicking technique. e.g. with well correspond parameters Punching measurement prior studies using alternate yielded of system calibration The approaches. of 0.85. coefficient a correlation Analysed variables Analysed maximal force [N] punching force [N] impact force [N] time [s] execution Impact force [N], time [s], impactExecution time [s] maximum force [N], reaction time [s] of a punch [ms], duration of a punch [N], ICC force energy [J] force [kN], power [W], height [m]. torque [Nm]; peak joint max force [N]; and force-velocity power-velocity relationship [vpm], punching bag reaction force [N] voltage [V],force [N], acceleration [g], power [W]velocity [m/s], Procedure the head with max effort punches to Straight either bouts, boxing competitive during simulated in punch combinations, singly or in 2 3 straight an audio cue. from sequence a prescribed ring in front held in the boxing matches The was Each fight each fight. for of a crowd 6 Totally and judged. refereed professionally matches. boxing the considering recorded 2 trials of 3 distances, and, leg length (medium distance) subjects’ and distance) 1/3 up the leg (large respectively, the leg (short1/3 down distance). are can when you and fast as you strong ‘‘as Kick short 25–30 in medium, long, distances. ready’’ 2 min between kicks; between of rest seconds each distances. for 2 kicks distances. with the rear 3 single punches (both techniques) max punching develop hand and lead to force. with the lead leg and (both techniques) 3 kicks force. maximal kick develop leg to rear with On the visual signal punch execution 2 series with 10 bag. the boxing towards step and 2 series with between) punches (30 s break between) 10 punches (10 min break with maximal energy. least 3 trials of kick At muscle CMJ and SPJ, plate Jump on the force F-v of punches and kicks, force strength, punch, 3 trials of 3 trials of straight relationship. and side apdolio kicks hook punch, 3 apdolio kikcs of a fight. with both legs during 120 s simulation leg also during with the rear dwit chagi kicks And of a fight. 120 s simulation Single punches during 1 min using the dominant with system measurement hand against the static system. the dynamic measurement

- Limbs involved Both Both One One Both Both hand Lead hand (1) rear (2) both legs Dominant hand (rear)

Task (straight Punching punch) (various Punching types) Kicking (bandal chagui, kick) roundhouse Kicking kick) (roundhouse Punching hook) (straight, (apdolio, Kicking dwit chagi) (direct Punching punch) kick) (front Kicking (1) Punching hook) (straight, (2) Kicking dwit (apdolio, chagi) Punching To assess the reliability parameters of parameters assess the reliability To device a „Box-check” Aim of a tri-axial Development of dynamometer capable boxing different between discrimination punch deliveries. during assess the punch forces To matches boxing professional and the impact examine force To whether the execution explore to affects impactdistance kicking force time. and execution the max impact force, Compare and impact time, time in execution to the head in relation to the kicking and weight distance the execution competition the athletes’ to according level design a new To measuring punching and device the replace could that forces kicking gauge-strain based measurement used formerly. system to design and construct test a kick To and displacement the force measure kicking of a verticalsubjected to target of the kick. energy total and calculate biomechanical examine To athletes characteristics of taekwondo and punches their kicks comparing of muscle with laboratory tests and power. strength non-embedded in-glove investigate To device. measurement Source Smith M et al. (2000) [16] J et al. Pierce (2006) [8] C et al. Falco (2009) [14] I et al. Estevan (2011) [10] L et al. Buśko (2016) [1] Šiška L et al. (2016) [20] Ramakrishnan K et al. (2017) [21] K and Nikolaidis Buśko PT (2018) [15] A and Jovanovski A Stappenbelt (2020) [5]

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in straight punching the reaction time of female The influence of expertise boxers were significantly longer while delivering the Generally, the force of punch was increasing punch with rear hand in comparison to lead hand with the level of expertise. The highest -max (0.619 ±0.025 s vs. 0.512 ±0.066) [1]. imum punch forces recorded in the included studies were 6900 N [20] in male boxer who The influence of task: kicking completed at least 3 competitive boxing matches, In kicking, five types of techniques were assessed: 5771 N [16] and 5358 N [8] in elite boxers. The front kick, apdolio, dwit chagi, yop chagi and bandal lowest maximum punch forces were recorded in chagui while the technique of front kick and ban- novice and were equal to 3845 N [5]. The mean dal chagui were not described in the text. Apdolio peaks punching force were significantly greater was a roundhouse kick, which is used to attack, in elite than intermediate, and intermediate than defend or counter-attack the opponent. The dwit novice (rear hand: 4800 N >3722 N >2381 N, chagi was a back kick in which the athlete turns lead hand: 2847 N >2283 N >1604 N) [16]. In the body away front the target and pushes the roundhouse and bandal chagui kicking, expert back leg straight toward the target, hitting it with taekwondo athletes had higher mean impact a heel while watching over the shoulder. And forces (1994.03 N ±537.37) than novice finally the yop chagi was a side kick during which (1477.90 N ±679.23) [14]. The elite taekwondo the athlete rises knee of kicking level, straighten athletes were also better than novice when the toward the target throughout sagittal plane so that distance from the target was extremely short the heel and the outside of foot strikes the target. (elite 1829 N ±161 vs novice 1329 N ±167) or long (elite 1760 N ±149 vs novice 1203 N The mean force in front kick varied from 1170 N ±154). In addition, the significant difference in to 7790 N and the front kick energy from 34 J peak forces delivered by front kick was found to 178 J with the 67% of the participant of mean between trained in martial arts (5200 N) and energy above 100 J. No comparison between left untrained participants (3200 N) [21]. and right leg was presented [21]. In contrast, according to [8], boxing experience, According to [1, 15] the force of the apdolio kick measured by the number of professional bouts delivered with rear leg was significantly greater than and the boxing success (measured by the per- the kick delivered by lead leg (1206.7 N ±239.5 vs. centage of previously won bouts) were not a sig- 2072.3 N ±472.2 and 965.3 N ±234.1 vs. 1511.6 N nificant predictor of a punch force during boxing ±271 [1], 3541.3 N ±113.3 vs. 3205.3 N ±965 [15]). match. In martial arts no difference was found The high impact forces of rear leg were associated between untrained and trained in energy deliv- with high joint torques of hip flexors and extensors. ered during a front kick, even when it was nor- In addition, strong relationship between force and malized to the body weight [21]. No difference in power in spike jump was observed for lead and rear kicking force was found between medallists and leg in apdolio kick [15]. non medallists when the distance from the target was average [10]. No significant differences in force (female: lead 2461.1 N ±494.7 vs rear 2490.3 N ±846.2 and The influence of body weight male: lead 3514.6 N ±1190.4 vs rear 3426.1 N The significant correlation between participant’s ±911) and reaction time (female: lead 0.671 s weight and front kick energy and mean front kick ± 0.166 vs rear 0.716 s ±0.075 and male: lead force was found, however this relationship was 0.694 s ±0.078 vs rear 0.693 s ±0.080) were not linear [21]. Interestingly, in the study of [14, found between lead and rear leg for dwit chagi 10] the significant correlation between weight and kick [1]. According to [15] the force delivered by kicking force was found in novice taekwondo ath- the rear leg during dwit chagi (3568 N ±1306) was letes (non medallists), however was not found in slightly higher than the one delivered by apdolio elite (medallists). According to the same authors, (3541 N ±1130.3). the elite athletes generate greater impact forces due to the use of principle of kinetic chain, while The differences between right and left lower limb the non-elite compensate technique deficien- has been found in peak force delivered during yop cies with the use of their bodyweight. However, chagi (right: 9015 N ±2382, left 8294 N ±2308), the study of [16] showed that the greater mass mean force (right 4426 N ±2110, left 4454 N ±2293) of novice boxers did not lead to higher punch and stroke impulse (right 38 Ns ±13, left 42 Ns ±15). forces obtained by novice when compared to elite

athletes. These results indicated that using of body while delivering a punch to inanimate object. weight in novice was not a enough to compen- Similar results were observed in the kicking per- sate the effect of poor technique on final impact formance, where the peak forces were greater for forces. No influence of body weight on punch- the test of an individual kick than in a 120 s simu- ing forces was also shown in the study of [8]. The lated fight [15]. In contrast, in the study of [5] the mean impact forces delivered across different average punch force in novice boxers were twice weight categories were not significantly correlated higher than in the study of Pierce et al. [8] and with elite boxers’ body mass [8]. The highest mean were equal to 2310 N ±3280. These values were punch forces were observed in Light Middleweight greater than when the athletes were instructed (1149.2 N) and Light Welterweight (1124.3 N), to deliver a single punch to boxing bag or impact while the lowest in Super Middleweight (866.6 N) plates [1, 15]. and Cruiserweight (920.5 N). Similarly, the cumula- tive punches force which is the function of punch force, number of punches delivered and the num- DISCUSSION ber of rounds showed no relationship with boxers’ weight [8]. The presented study reviewed recent information regarding the usefulness of sport-specific devices The influence of gender dedicated to measure striking force in combat Four of ten included studies involved female sports (martial arts) athletes. Overall, the most and male participants, however in two of them of the included studies showed the significant the comparison between genders was not pre- influence of gender, level of expertise and the sented [20, 5]. The intergender differences have striking technique on the impact forces associ- been found among boxers and taekwondo prac- ated with punching and kicking. However, these titioners. In boxers, the differences between results must be interpreted with caution due to male and female where observed in force (female the large diversity of measurement systems, used 1170.7 N ±165.3, male 1592.5 N ±507.1) and sensors and the environment in which assess- reaction time (female 0.619 s ±0.025, male 0.528 ment has been done. s ±0.068) of straight punch delivered by rear hand. In taekwondo, the higher impact forces and In the majority of included studies, the strik- shorter reaction time were observed in male sub- ing performance was assessed in non-ecolog- jects when apdolio kick was delivered with the rear ical conditions. It means, that the punch/kick leg (impact forces: female 1511.6 N ±271, male was performed in decontextualized situation 2072.3 N ±472.2, reaction time: female 0.682 s and was not related to the sport practiced [23]. ±0.058, male 0.631 s ±0.066) and lead leg (impact Isolated striking to non-moving object were forces: female 965.3 N: male 1206.7 N, reac- assessed by the target-based measurement tion time: female 0.718 s ±0.084, male 0.644 s devices, such as punching bags, boxing manikins ±0.064) [1]. Similarly, the force of dwit chagi kick or impact plates. This restriction is not trivial, delivered by rear (force: female 2490.3 N ±846.2, since some studies have shown, that the punch male 3426.1 N ±911) and lead leg (force: female forces observed in ecological conditions (e.g. 2461.1 N ±494.7, male 3514.6 N ±1190.4) dis- during boxing match) were lower when com- tinguished male and female participants [1]. pared to the ones observed in non-ecological According to [21] gender had strong influence on context [8, 15]. Previous authors [8] highlighted the kick energy, even if it was normalized to the that in the ring, the target is a living object, who body weight of the subject. can avoid a punch completely, partially evade it to reduce the force of impact, or receive the The influence of experimental conditions punch before optimum reach. Thus, the dynam- The results of punch force during boxing matches ics of the ring reflect a considerably different were not straightforward. According to [8], the task than that of a laboratory simulation. The average values of punch force during matches assessment of the impact forces in sport-spe- varied from 920.5 N ±508.5 in cruiserweight to cific conditions opens up new possibilities in 1149.2 N ±665.8 in light welterweight (the other analysing and refereeing combat sport perfor- weight categories: junior lightweight, super mid- mance. For example, it could objectify the ref- dleweight, heavyweight with values in between). eree decisions and assign points depending on These results indicated lower values of punch the punch impact force delivered by an athlete forces obtained during boxing matches than during match [8, 11].

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In most of the studies included, the punch or kick At last, reviewed articles showed that several was delivered to an object which is not comparable papers did not include proper statistical descrip- in mass and biofidelity to the human body [24, 25]. tion (e.g. did not report effect sizes) and none What is more, many of the strike measuring devices of the studies included sample size justification. have resulted in values that do not fully reproduce Comparisons were based on small sample sizes, the attacking force and multidirectional compo- what in turn could infer statistical results and nents of a strike, nor do they consider the dynamic influence author’s conclusions. repeated nature of combat sport. Generally, it is difficult to find consistencies in research on the impact force of various punches or kicks. As highlighted CONCLUSIONS by previous authors, there are several possible rea- sons for it [18, 14, 15]. First is the variation in the Current review revealed that there are plenty striking technique. Another issue is the type of pad- of valid, accurate and reliable devices which ding material used in boxing gloves or target-based opens up new possibilities in enhancing combat measurement device. On the one hand, the high- sport training and performance. Unfortunately, est impact forces would be obtained while deliver because of the large methodological and tech- a strike to non-padded, rigid object. For example nological diversity, the results obtained by pre- a kick on a concrete wall would produce greater vious authors cannot be directly compared. impact force in comparison to a kick delivered to That is why, the future research perspectives a soft foam [21]. On the other hand, delivering should include the evaluation of diverse groups a maximum strike to a stiff object could result in of athletes across different force measurement increased risk of injury. Third reason might be the devices. This approach would allow for estima- size of the target which also varied between studies. tion of the measurement differences resulting According to Fitts’ law, the size of the target deter- from the device construction. mine the movement velocity and consequently may influence the striking force [26]. Thus the size, elas- ticity or inertia of the target have a strong impact HIGHLIGHTS on the evaluation of the impact force [24, 18, 14]. • The devices dedicated to measure the force of Moreover, the measurement equipment used strike were equipped with in-built set of piezo- to register the data, as well as the mathematical resistive sensors or strain gauges. model implemented to calculate eligible variables, has a direct influence on the final value of impact • Assessment of striking forces based on accelera- force. Therefore the data obtained from different tion data shows the measurement error less than types of force sensors (strain gauge, piezoelectric 1% in comparison to strain gauge measurements. sensors, S-type Dacell load cell) should be compared with cautions with the force values calcu- • The elite athletes generate greater impact forces lated on the basis of accelerometer data. However, in kicking due to the use of principle of kinetic in [1], verification of method accuracy revealed chain, while the non-elite compensate technique that the measurement force error in accelerome- deficiencies with the use of their bodyweight. ter-based approach was less than 1%.

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Cite this article as: Akbaş A, Brachman A, Gzik B et al. The objective assessment of striking force in combat sports using sport-specific measurement devices – a review. Arch Budo 2021; 17: 205-216

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