Training & Testing Thieme Kohiruimaki Ren et al. Suspended Push-up Training Aug- ments … Int J Sports Med 2019; 00: 00–00 Suspended Push-up Training Augments Size of not only Upper Limb but also Abdominal Muscles Authors Ren Kohiruimaki1, 2, Sumiaki Maeo3, Hiroaki Kanehisa4 Affiliations ABSTraCT 1 Sports and Life Science, National Institute of Fitness and We investigated the effects of sling-based, suspended push-up Sports in Kanoya, Kanoya, Japan training on muscle size and function of upper limb and ab- 2 Metropolitan Police Department, Tokyo, Japan dominal muscles. Eight men conducted suspended push-ups 3 Research Organization of Science & Technology, to failure 3 sets/session, 3 sessions/week, for 8 weeks. The Ritsumeikan University, Kusatsu, Japan maximum number of push-ups during training gradually and 4 Faculty of Sport and Health Science, Ritsumeikan from the first to last training session ( + 92 %), suggesting im- University, Kusatsu, Japan proved muscle endurance. After the training, muscle thickness of the elbow extensors ( + 16 %) and flexors ( + 3 %), as well as Key words abdominal muscles (rectus abdominis: RA, + 27 %; external muscle thickness, isometric strength, one-repetition oblique: EO, + 14 %) significantly increased. No changes oc- maximum, training to failure, electromyography curred in maximum isometric strength of elbow extension or flexion, nor in 1-repetition maximum bench press. In a follow- accepted 20.07.2019 up experiment, electromyograms (EMGs) of RA, EO and inter- nal oblique (IO) during suspended push-ups to failure were Bibliography measured and normalized to those during maximum voluntary DOI https://doi.org/10.1055/a-0989-2482 contraction of each muscle ( % EMGmvc) in six men. EMG sig- Published online: 2019 nificantly increased when reaching failure in all muscles (RA: Int J Sports Med 46–88 %, EO: 32–50 %, IO: 19–52 %, start-end), and was par- © Georg Thieme Verlag KG Stuttgart · New York ticularly high in RA. These results suggest that suspended push- ISSN 0172-4622 up training can augment size of not only upper limb but also abdominal muscles, likely attributable to high muscle activities Correspondence during exercise; however, this does not necessarily improve Dr. Sumiaki Maeo maximum strength after training thus warrants careful inter- Research Organization of Science & Technology pretation/application. Ritsumeikan University 1–1–1 Nojihigashi 525–8577 Kusatsu Downloaded by: Glasgow University Library. Copyrighted material. Japan Tel.: + 81/77/561/2791, Fax: + 81/77/561 3761 [email protected] Introduction to be effective in improving muscle function [5, 7, 8, 10]. For exam- Training of the trunk musculature, the abdominal muscles, in par- ple, Dannelly et al. [7] demonstrated that a combination of 10 types ticular, has become an essential facet of many training programs of sling exercise training (e. g. suspended push-up) in untrained fe- [1]. The main reason behind this is that greater trunk stability is males was equally as effective as traditional resistance training for suggested to benefit athletic performance by providing a founda- increasing strength [e. g. one-repetition maximum (1RM) bench tion for greater force/power production in the limbs [2]. For this press]. It is also reported that throwing velocity in female athletes purpose, instability resistance exercise using unstable surfaces and (handballers and softballers) was significantly increased after a devices [1–3] has been increasingly implemented, because this combination of 5–9 types of sling exercise training [9, 10] but not type of exercise is known to induce greater muscle activity (i. e. after their traditional resistance training analogs [9] or regular training stimulus) in trunk muscles compared to normal (stable) (sport-specific) training [10]. A recent study by Lima et al. [8] ex- exercises due to increased demands of stabilization [4–6]. amined the effect of suspended push-up training performed alone Sling exercise is one of the most frequently implemented and (without other sling exercises) on muscle function, showing supe- studied instability resistance exercises [4–10], and has been shown rior improvements over stable push-up training for muscle (push- Kohiruimaki R et al. Suspended Push-up Training Augments … Int J Sports Med Training & Testing Thieme up) endurance and chest press strength. These results collabora- tially influential) injuries before the study intervention. No injuries tively support the efficacy of sling exercise training. and/or dropouts occurred through this study. Participants visited While the above findings are all important, what is lacking to the laboratory and were fully informed about the purpose, proce- date is the key information regarding the putative effect of insta- dures and possible risks involved in the study, and provided writ- bility resistance exercise; does it actually train the trunk, or in par- ten informed consent. All participants experienced and were famil- ticular, abdominal muscles? Although some studies cited above re- iarized with the suspended push-ups and other tasks involved in ported gains in chest press strength [8] or 1-RM bench press [7] testing before data collection. This study was approved by the local after sling exercise training, which may be partly attributable to ethics committee, and was conducted in accordance with the eth- enhanced function of trunk including abdominal muscles, no con- ical standards of the IJSM [13]. vincing evidence exists supporting this theory. Examining changes in size of abdominal muscles can shed light on whether these mus- Experiment 1: Training intervention cles are actually trained by instability resistance training, which Training program would be of great interest to many training/rehabilitation practi- Suspended push-up training was conducted 3 sets/session, 3 ses- tioners and researchers. Furthermore, clarifying the effect of insta- sions/week, for 8 weeks by using a Redcord Trainer (Kilsund, Nor- bility resistance training on size and strength of the limb muscle way). In a prone position with the shoulders abducted at 90 ° and that was mainly involved in the exercise (e. g. the elbow extensors elbows fully extended (~0 °), participants grasped the grips with in suspended push-ups) would be also useful in identifying mech- both hands at the width slightly (plus one palm for each side) wider anisms underpinning a potential performance improvement, which than the shoulder-width. The toes were placed shoulder-width has also never been examined. apart on a wood base so that the height of the hands and toes were The main purpose of this study therefore was to investigate the horizontal. The pelvis was raised off the floor with the body weight effect of sling exercise training on size and function of abdominal distributed on the hands and toes [6], and participants repeated and upper limb muscles (Experiment 1). To this end, we designed push-ups to failure at a rate of 45 per minute based on a metro- 8-week suspended push-up training. This exercise was chosen be- nome. Participants were instructed to keep the trunk straight dur- cause it was performed in all of the previous studies that conduct- ing the whole movement and lower the body until the elbow was ed sling exercise training cited above [5, 7, 8, 10], and can be con- flexed at 90 °, and then return to the original position. The exercise sidered as the representative sling exercise. Additionally, we as- was discontinued when participants could no longer keep up with sessed muscle activity levels of abdominal muscles via the tempo. 2-min rest intervals were taken in between sets. A rest electromyogram (EMG) during the exercise to provide information period of 2–3 days (~48–72 h) were taken between sessions. Num- regarding exercise intensity for these muscles (Experiment 2). We ber of push-ups (repetitions) performed per set was recorded hypothesized that 1) 8-week suspended push-up training would throughout all training sessions, and maximum number of repeti- increase size of not only upper limb but also abdominal muscles, tions (REPmax) for each session, which was always observed in the and 2) activity levels of abdominal muscles during the exercise first set, was reported as an index of muscle endurance. would be sufficient to induce hypertrophy (e. g. > 40 % of maximum activation [11]). Measurements Before and after the training intervention, indices of muscle size and function were measured. Rest periods of 1–2 days and 2–3 days Materials and Methods were taken between the pre-test and first training session and be- tween the final training session and post-test, respectively. All Downloaded by: Glasgow University Library. Copyrighted material. Experimental design measurements were conducted on the right side of the body, and The sample size for Experiment 1 was calculated on the basis of an the following variables were obtained: α-level of 0.05, a power (1 − β) of 0.80, and a 20 % change (effect size = 1.2) in muscle thickness of an abdominal muscle after 8-week Muscle thickness B-mode ultrasound apparatus (Prosound 2; abdominal bracing training [12]. This revealed that eight partici- Aloka, Tokyo, Japan) was used to measure muscle thickness of the pants would be needed to detect a significant change in muscle elbow extensors (EEs), elbow flexors (EFs), rectus abdominis (RA), thickness (G * Power; Heinrich- Heine-Universität Dusseldorf, Dus- external oblique (EO) and internal oblique (IO) at rest by the same seldorf, Germany). For Experiment 2, the sample size was not cal- procedure used in previous studies [12, 14–16]. Briefly, muscle culated because it was a follow-up experiment, the purpose of thickness of the upper arm muscles was measured at 60 % of the which was to provide supportive information regarding exercise distance down from the acromial process to the lateral epicondyle intensity. Eight and another (different) six healthy male university of the humerus, and included the long and medial heads of the tri- students majoring in physical education participated in Experiment ceps brachii for the EEs, and the biceps brachii and brachialis for the 1 and 2, respectively.