The Biceps Brachii Role in the Stabilization of the Cross Punch

Marco Prenassi et al., IJSMR, 2020 3:13

Research Article IJSMR (2020) 3:13

Internal Journal of Sports Medicine and Rehabilitation (ISSN:2637-5044)

The biceps brachii role in the stabilization of the cross punch

Marco Prenassi1 , Renato D. Donato2,3 , Simona Mrakic-Sposta4* , Lorenzo Rossi5, Luca Andreoletti3, Alessandra Vezzoli4, and Sara Marceglia6

1UO Neurofisiopatologia, Fondazione IRRCS Ca’Granda Ospedale Maggiore Policlinico, Milan, Italy; 2Heracles Gymnasium SSD s.r.l. Fortitudo ETS, Milan, Italy; 3Dipartimento di Scienze Biomediche per la Salute,Università degli Studi di Milano, Milan, Italy; 4Institute of Clinical Physiology, National Research Council, IFC –CNR, Milan, Italy; 5Newronika s.r.l.;6Dipartimento di Ingegneria e Architettura, Università degli Studi di Trieste, Trieste, Italy

ABSTRACT

Purpose: starting from an injury background, we assumed that *Correspondence to Author: the biceps brachii’s activations could have an important role in Simona Mrakic-Sposta upper limbs injury. In this work we analyzed whether different Institute of Clinical Physiology, activations of the biceps brachii impact on the power transfer National Research Council, IFC – of the punch and how boxers of different skill levels activate the CNR, Milan, Italy biceps brachii when deliver a punch according to their skill level and efficacy. How to cite this article: Methods: we enrolled, basing on official rankings, 23 skilled Marco Prenassi, Renato D. Donato, (n=6) and unskilled boxers. Subjects were instructed to perform Simona Mrakic-Sposta, Lorenzo three cross punches directed to a fixed elastic target triggered Rossi, Luca Andreoletti, Alessan- by the coach whistling, and were monitored through a surface dra Vezzoli, and Sara Marceglia. electromyography sensor (EMG) on the biceps brachii to The biceps brachii role in the stabi- estimate the muscular activation during the performance, and lization of the cross punch. Internal through an accelerometer placed inside the elastic impact target Journal of Sports Medicine and Re- to estimate the impact energy. We analyzed the oscillatory habilitation, 2020; 3:13. content of the EMG signal in order to assess the muscular activation between skilled and unskilled boxers, and between weak and strong punches. Results: both skilled and unskilled boxers threw strong, medium eSciPub LLC, Houston, TX USA. and weak strikes. Skilled boxers performed better than unskilled Website: https://escipub.com/ boxers (47% vs 25% in the “strong punch” category).The EMG analysis revealed a significant increase of lower and higher frequencies (2-4 Hz and 15-17 Hz) and a decrease on the

IJSMR: https://escipub.com/internal-journal-of-sports-medicine-and-rehabilitation/ 1 Marco Prenassi et al., IJSMR, 2020 3:13 medium frequencies (7-9 Hz) in the skilled boxers compared to the unskilled boxers in strong punches. Weak punches had a similar activation patterns in the two groups. Conclusions: our results support the hypothesis that skilled boxers adapt their activation pattern of the biceps to better stabilize the punch delivery (and thus increasing the transfer of force).

Keywords: Boxing; Biceps brachii; EMG analysis; Punch; Shoulder injury; Tendon detachment

Introduction impact. It is supposed that expert boxers can Boxing discipline is a sport characterized by generate more impact force compared to novice many traumatic phenomena. Indeed, the fighters boxers, and more impact force means an in- have to absorb the impact of the blows, to the creased stress to the throwing arm. head and the body, thrown by the rival but also, These force impacts, generated by the punch they have to absorb the impact of their own when hits the target, stress the upper limb joints. punches. Self-inflicted hand injuries could arise Studies on these impact forces managed to from these latter impacts. demonstrate that, during the impact, the high ac- Many studies investigate direct injuries to the tivation of flexor and extensor muscles, recruited hand and the head caused by the traumatic fist to close the hand, produce a shot with 55% more events. In particular, they focused on concus- strength compared with a shot without clenched sions, in short and long terms [1,2,3] and also on hand. The high muscle activation reduces inju- metacarpal injuries [4,5,6,7]. Not less important, ries, metacarpal joint deformation, and in- however, is the indirect trauma, caused by repet- creased power transfer to the target. [10] The sta- itive training sessions, to the muscles and ten- bilizing muscle action generated by the impact dons. The impact overload can direct the ath- on the target appears to be an involuntary kind, letes to have tendinopathy, muscle tears, and, at where the term “involuntary” is a not reflective worst, tendons detachment. Novice boxers have event in line with the act’s finality. been shown to have fewer shoulder injuries than Exactly as the insights of Eugéne Minkowski experienced boxers; this statistical evidence in ’57 when he described the body muscle com- supports the idea that indirect trauma injuries, pensation to keep the orthostatic position, which caused by functional overload, are no less im- is in a continuous strain by perturbative force. [11] portant than direct trauma injuries. Shoulder in- The body implements continuous compensation, juries etiology by overload training can be identi- without a real consciousness, intrinsically moti- fied in the defective movement of the blow. In- vated, and intentioned, to reach the aim. As de- correct movement patterns can stress the shoul- scribed by Minkowski E. (1957) and Lacquaniti & der and set movement patterns characterized by Maioli (1989), the researches have shown that scapular dyskinesia with an increase of extra-ro- there are many anticipatory muscle activations, tation [8]. Moreover, it can add an inaccurate con- without the perception of consciousness, to sta- trol of scapular muscle and a bad activation of bilize posture and thus be able to initiate con- the serratus anterior that can create a scious action [11,12]. sub-acromial impingement. [9] Not only imperfect An intentional impact, like a blow or a support- skills are dangerous for athletes' structures; a foot under a jump, produces necessarily an in- perfect shot still increases the overload of the voluntary muscle act to avoid unexpected results.

IJSMR: https://escipub.com/internal-journal-of-sports-medicine-and-rehabilitation/ 2 Marco Prenassi et al., IJSMR, 2020 3:13 This unconscious activation must be precisely involving the hips, torso, and upper arm, in which tuned to the gesture to be performed. When the weight is transferred from the rear foot up to there isn’t tuning among anticipatory/compensa- the knuckles of the hand [18]. tor muscle activation and finality act, there is the Nakano et al, (2014) [19] suggests that the im- probability of failure of the qualitative gesture or, pulse of the cross punch to the face is more de- in the worst, injuries.We can have a striking ex- pendent on the final pre-impact momentum of ample in the fright and pain experienced during the punching arm rather than the momentum of the loss of the last step when people go down the other body segments, so its extension before the staircase without attention. The fails of antic- the impact is vital in delivering a “strong” punch. ipatory muscle activation obligate the body to In this complex action, the biceps brachii may be compensate for the surprise of the impact force involved in dampening the extension velocity of with the ground with the massive recruit of an- the arm, limiting the impact force of the punch, tigravitational chains and with a possibility of se- or, after the impact; it may contribute to stiffening vere injuries to the back. Recent studies showed the arm and consequentially increasing the en- that the repeated impact force, arise from the ergy transfer. In this work, we also argue that this foot support on the ground, generates electro- stiffening motion could be linked to the inflamma- myographic variances of the muscle activities to tion of the long head of the biceps brachii. decrease soft tissue vibration [13] and the over- To better understand the role of the correct mod- load tendon muscle. [14] This evidence supports ulation of the biceps brachii activation in the the idea that to the increment of the impact there cross punch stabilization, in this study we aim to: is an increase of muscle recruit to reduce the a) assess whether different activations of the bi- overload of the joint and the tendon muscle ceps brachii impact on the power transfer of the structures. punch; b) analyze how boxers of different skill The constant repetition of massive recruitment levels activate the biceps brachii when deliver a and hard force expression, generated from the punch according to their skill and efficacy. To do repetitive specific workout, could be the principal so, we neurophysiologically analyzed the re- cause of upper arm injuries, including long head sponse of the biceps brachii while boxers of dif- brachii biceps muscle [15,16]. It is not infrequent ferent skill levels were executing a cross punch, that boxers report pain shoulder near the proxi- by measuring the activation of this muscle with a mal attachment and, mostly in the heavyweight bipolar superficial electromyogram (EMG) and class, can suffer the laceration or complete de- an accelerometer inside an elastic target to as- tachment of the distal attachment. In the study sess the impact force between punches. conducted by Siewe et al, (2015) on boxing com- Materials and Methods petition, the most frequent injuries, not including Twenty-three boxers were enrolled in this study the injuries to the head, involve the upper limbs. and divided into two groups (skilled-unskilled) [17] For this reason, it’s important creating fo- using the Italian Boxing Federation (FPI, Feder- cused training programs, that can help the power azione Pugilistica Italiana), Association Interna- increase of muscle groups stressed by impact tionale de Boxe Amateurs (AIBA) Open Boxing force, could extend the boxer’s sports career, (AOB) score system [20]. We included in the and remove the risk of injuries [6,17]. skilled boxers with >80 scores. All subjects In boxing, the cross punch is a movement signed informed consent and were fully informed

IJSMR: https://escipub.com/internal-journal-of-sports-medicine-and-rehabilitation/ 3 Marco Prenassi et al., IJSMR, 2020 3:13 about the experimental procedure, according to After that, they were instructed to perform three the declaration of Helsinki. cross punches directed to a target upon hearing After a baseline assessment to measure height, the coach whistle, using the regulated hand weight, and contracted biceps (bicepsC) circum- wraps and boxing gloves [21]. The elastic target ference, boxers were asked to perform a Maxi- was made by a wooden plate surrounded by an mum Voluntary Contraction (MVC) task that was elastic rubber to absorb the impact (Figure 1). used as reference for subsequent analyses.

Figure 1. Experiment setup, boxer position and target.

At least 40 seconds elapsed between each start- impact, as the energy transferred by the punch ing signal (whistle). A 256 samples/s bipolar to the target. A visual analog scale of pain (VAS) EMG, with one electrode placed at the origin and was administered before and after the session, the other one at the insertion of the biceps bra- to assess the presence of pain and the area chii, was used to record muscle activity during where the pain was predominant. the task. The reference electrode was applied to The punch impact was estimated through the ac- the lateral malleolus. A data-marker button was celerometer data placed within the target and pushed to trigger the recording to the coach calculated within a 10-sec window centered on whistle. A three-axial accelerometer acquiring the maximum absolute peak of acceleration. We data at 100 samples/s (Shimmer Sensing IMU) estimated the relative energy transferred by the was placed inside on the wooden plate, on its punch with this formula: longitudinal axis of mass, in order to record the

푖=0 where 푟퐸푘 is the signal of relative energy, 퐸푘 deformations of the target, since it was regarded is the kinetic energy, m the mass of the target as a minor component during the trials (the tar-

(the target is the same for every boxer), 푎푖: in- get accelerometric response was tested on the stant acceleration detected by the sensor and 퐹푠 floor, dropping a ball weight of 5 kg at 1 meter is the sampling frequency (100 samples/s). We before and after the experiment, the results were omitted the energy absorbed by plastic comparable within 2% of the total power).

IJSMR: https://escipub.com/internal-journal-of-sports-medicine-and-rehabilitation/ 4 Marco Prenassi et al., IJSMR, 2020 3:13 The biceps brachii activation was estimated punch window. This is represented by the power through the EMG signal recorded during the ex- spectrum of the EMG signal calculated using the ecution of the cross punch. More specifically, the Welch method [22] which shows the predominant full rectified EMG signal was normalized by its frequencies in the EMG signal. We considered MVC. We selected the cross-punch EMG win- the envelope of the EMG as smoothing the rec- dow using the data marker trigger as initial point tified signal with a low pass filter [23] with a time (corresponding to the whistle). The end point constant of 4 ms. was selected as the instant in which the signal, Punches were sorted according to the skill level smoothed with an average mean filter by 256 of the boxer (skilled and unskilled) and by their samples, crossed its standard deviation (calcu- relative kinetic energy, to categorize “strong”, lated on the entire recording). To assess the ac- “weak”, and “medium” punches, according to the tivation of the biceps brachii, we analyzed the os- following 2 thresholds (Figure 2): cillatory content of the EMG signal in each cross-

Figure 2. Relative punch energy per subjects, grouped by skilled/unskilled boxers and with strong, medium, weak punch thresholds.

Where 푠푡푑 is the standard deviation.

Table 1

IJSMR: https://escipub.com/internal-journal-of-sports-medicine-and-rehabilitation/ 5 Marco Prenassi et al., IJSMR, 2020 3:13

Table 2

Table 1 shows the number of punches associ- recorded from the target. More specifically, we ated for each category. We therefore compared performed a coherence analysis between the the oscillatory activities of the EMG signal in power spectra of the accelerometric raw signal skilled and unskilled boxers and in strong, me- and the EMG envelope on the whole cross dium, and weak punches. punches. Then, to rule out the presence of impact arte- Finally, we compared the pain perception in facts, affecting the estimation of biceps brachii skilled and unskilled boxers measured through activation, we verified the relationship between the VAS, by applying a Wilcoxon-Mann-Whitney the signal recorded from the muscle and that test (p<0.05).

Figure 3. Mean MVC EMG power density spectrum between the categories (“Strong” punches, “Medium” punches and “Weak” punches) and the skill level (Skilled and Unskilled). The magenta and green areas are differences of statistical significance: p<0.05, Wilcoxon-Mann-Whitney test.

Results punches 7 were discarded due to a sensor mal- Six boxers were enrolled in the skilled group functioning. In total, we analyzed 53 punches, 17 (AOB score mean 140.4, standard deviation: for the skilled group and 36 for the unskilled 55.6), and 14 in the unskilled group (AOB score group. Table 2 shows that the circumference of mean 11.5, standard deviation: 19.5). Three the biceps (BicepsC) is not correlated with the were discarded due to data loss. Of the 60 strength of the punch (mean rEk) for each boxer.

IJSMR: https://escipub.com/internal-journal-of-sports-medicine-and-rehabilitation/ 6 Marco Prenassi et al., IJSMR, 2020 3:13 Also, we found 14 weak punches (of which 2 be- other part of the body by all the boxers. longing to skilled boxers), 22 medium punches Discussion (of which 7 belonging to skilled boxers), 17 In this preliminary study, we showed that the strong punches (of which 8 belonging to skilled contribution of the biceps brachii to the cross boxers). Table 1 and Figure 2 show that, even if punch differs between skilled and unskilled box- the skilled group tends to strike with superior ers, especially in strong punches, thus support- force, not all motions are stronger than the un- ing the hypothesis that a correct modulation of skilled counterpart. the activation of this muscle is crucial for improv- We therefore analyzed the activation of the bi- ing the punch efficacy. ceps brachii according to the skill level and to the Our results show a notable increase in the skilled strength of the punch (Figure 3). group on the low frequencies (2-4 Hz) and the We found that in the “strong punch” category, high frequencies (15-17 Hz) in strong punches there is a higher EMG activation in the 2-4 Hz but not in weak punches, in which the two groups and in the 15-17 Hz oscillatory ranges in skilled show a similar activation pattern (the EMG 6-8 boxers compared to unskilled boxers. Con- Hz peak is present in both groups). In the “strong versely, the “weak punch” group is characterized punch” category, this peak at 6-8 Hz is present by an oscillation at 6-8 Hz, both in skilled and only in the unskilled group. The activation of bi- unskilled boxers. Notably, this peak is also pre- ceps brachii is suggested to change in the me- sent in the “strong punch” in unskilled boxers, dium group, where the central frequencies tend but not in skilled boxers (p<0.05, Wilcoxon). to decrease in the skilled group compared to the In the “medium punch” category, we observed a unskilled group. These different patterns could difference in biceps brachii activation between also be linked to the inflammation of the long the skilled and unskilled group in low and high head of the biceps brachii, a common occur- frequencies (2-4 Hz and 15-17 Hz), similar to rence in boxing. that of strong punches, even if not statistically This inflammation is often associated to a limited significant. Then, the results of the correlation articular mobility of the scapula and to a strong analysis aimed to rule out the presence of impact intra rotation of the shoulder caused by the spec- artifacts in signals, showed an high coherence ificity of the athletic gesture. The etiology of this (mean magnitude squared coherence estimate > inflammation is thought to be associated to an 80% ) at 1 Hz, 5 Hz, 9 Hz, 14 Hz and 19 Hz, indirect phenomenon caused by a non-efficient suggesting possible artefacts, and a low coher- shoulder joint biomechanics. Our work suggests, ence (mean magnitude squared coherence esti- instead, that the inflammation can be caused by mate < 42%) in 2 Hz, 7 Hz, 14-16 Hz bands, thus the incorrect recruitment of the biceps brachii confirming the electrophysiological differences during strong punches. The performance model measured through the EMG.Three skilled box- of the punch needs to consider the different ac- ers reported a slight increase of pain in the tivation to reduce inflammations, elongations, punching hand (mean difference +2.14), while strains or muscle/tendons tears. only one unskilled boxer reported a slight in- There are however some technical limitations to crease (mean difference +0.714), with a signifi- be considered. First, the recording hardware cant difference between the two groups (EMG device with 256 samples/s sampling with (p<0.025). No pain increase was reported in only one channel) could not be synchronized

IJSMR: https://escipub.com/internal-journal-of-sports-medicine-and-rehabilitation/ 7 Marco Prenassi et al., IJSMR, 2020 3:13 with the accelerometer device thus preventing could be caused by the lack of conditioning and us from performing more in-depth analyses of strain-adaptation. This maximal recruitment of the correlation between muscle activity and im- the muscular district, caused by the impact pact. Second, EMG electrodes were placed fur- forces, could be a reflex contraction to safeguard ther away from each other, enabling possible the shoulder or humeroradial joint. A correct crosstalk with the triceps brachii; this was done training must therefore take into consideration in order to not impair the punch movement of the this dampening action. athletes. In the future, these limitations should In the light of this new performance model hy- be overcome in order to conduct studies aimed pothesis, to counterbalance the strong reflex ac- to characterize the EMG signals using a finer tion of the biceps brachii and to avoid injuries, timescale synchronized with the impact of the new complementary exercises could be added punch, and to analyze the precise activation of to the flexor chain of the daily routine of unskilled both biceps brachii and triceps brachii before boxers, focusing on the power modulation of the and after the hand contact with the target. shots on different boxing bags (light/me- In addition, the changes in the activation pattern dium/heavy) to gradually adapt both tendons to of the biceps brachii observed in the skilled the impact forces. group and the variation of the athletic gesture These complementary exercises could be either supports a philosophical thesis about learning general or specific. Examples of general exer- through selfimitation [24]. The skilled boxer, trying cises are: to find the most effective athletic gesture, is ca- 1. Slow curl with elastic tapes with antalgic func- pable of developing his/her punching method tion; thanks to an explorative motion that trough “trials 2. Curl with dumbbells with emphasis on eccen- and errors” have helped him/her to identify the tric phase to strengthen the frontal biceps; best technique for his/her corporeality. This vari- 3. Pull ups to strengthen the dorsal muscles and ability have an impact in the teaching technique the biceps brachii; which shouldn’t be strictly analytical but rather 4. Hand grip strength exercises; give room for a phase of “learning by error” to and of specific exercises: develop new boxing skills, with the final objective 1. Single punches to the heavy boxing bag of finding new methods that fit the psychophysi- searching for the adaptation on multiple impact cal characteristics of the boxer; that is accom- angle; plished with feedbacks of effectiveness and grat- 2. Power modulation of the hits with different ification. The analysis of muscular activity, and boxing bags (light/medium/heavy) to adapt grad- specifically of the biceps brachii, could guide the ually the tendon to the impact forces. trainer in understanding whether the athletic This strategy requires further studies aimed to gesture developed by the boxer is safe enough collect the long-term results of the proposed ex- in terms of possible inflammations or other ad- ercises in relation to the muscle inflammation, in verse effects. order to establish its efficacy in reducing inflam- Practical applications: Even if preliminary, this mation and injuries in unskilled boxers. In this study suggests that the frequent inflammation brief exercise, no pain increase was reported in phenomena, or in the worst case, the detach- that location, the predominant pain was located ment of the distal insertion of the biceps brachii, on the hand and relevant only in the skilled

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