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01.12.2015 | Research article | Ausgabe 1/2015 Open Access

BMC Musculoskeletal Disorders 1/2015

The effects of exercise type and elbow angle on vertical ground reaction force and muscle activity during a push-up plus exercise

BMC Musculoskeletal Disorders > Ausgabe 1/2015
Jun G San Juan, David N Suprak, Sean M Roach, Marc Lyda
Wichtige Hinweise
Jun G San Juan, David N Suprak, Sean M Roach and Marc Lyda contributed equally to this work.

Competing interests

All the authors declare that they have no competing interests.

Authors’ contributions

All the requirements for authorship have been met. JSJ and ML performed the data collection. DS participated in the design of the study and performed statistical analysis. SR participated in the design and conceptualization of the study. JSJ was responsible for writing the manuscript. All authors read and approved the final manuscript.

Authors’ information

Jun G. San Juan, PhD, ATC, is an Assistant Professor of Kinesiology at Western Washington University, Bellingham, WA, USA and is a certified athletic trainer. David N. Suprak, PhD, ATC, CSCS is an Associate Professor at Western Washington University in the Kinesiology program and is a certified athletic trainer and strength and conditioning specialist. Sean M. Roach, PhD, DPT, ATC, is a research associate at Western Institute of Neuromechanics which is a non-profit research organization based in Eugene, OR, USA. He is also a practicing physical therapist. Marc Lyda, MA, is a research assistant at Western Institute of Neuromechanics.



Proper alignment of the scapula during upper extremity motion is important in maintaining shoulder joint function and health. Push-up plus exercise is considered as one of the best exercise to strengthen the muscles that stabilize the scapula. The purpose of the study is to examine the effects of push-up plus variants and elbow position on vertical ground reaction force and electromyographical activity of four shoulder muscles during concentric contraction.


A total of 22 healthy subjects volunteered for the study. Each of the subjects performed both modified and traditional push-up plus. Modified push-up plus was performed with both knees and hands touching the ground while the traditional push-up plus was executed with hands and feet contacting the ground. Electromyography (EMG) of the upper trapezius (UT), lower trapezius (LT), infraspinatus (INFRA), and serratus anterior (SA), and vertical ground reaction forces (vGRF) were collected.


The traditional push-up plus exhibited higher EMG activity in all muscles tested (P < .05) and vertical ground reaction force (P < .001) compared to modified push-up plus. The highest difference in EMG activity between the two exercises was observed with the Serratus Anterior muscle (22%). Additionally, the traditional push-up plus presented a higher vGRF compared to the modified push-up plus (P < .001) by 17%. The SA had the greatest EMG activity compared to the other muscles tested during the concentric phase of the traditional push-up plus, and this did not occur during the plus phase of the exercise.


The highest activity of the serratus anterior occurred at 55° of elbow extension during the concentric phase of the traditional PUP and not at the plus phase of the exercise. This suggests that when prescribing an exercise to target the serratus anterior, a traditional push-up is adequate and the plus-phase is not necessary. However, for patients that cannot perform a traditional push-up, the modified push-up plus would be a great alternative to strengthen their serratus anterior.
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