Journal of Medical and Biological Engineering, 31(4): 289-293 289 Effect of Push-up Speed on Upper Extremity Training until Fatigue Hsiu-Hao Hsu 1 You-Li Chou 2 Yen-Po Huang 1 Ming-Jer Huang 1,3 Shu-Zon Lou 4 Paul Pei-Hsi Chou 5,6,7,* 1 Department of Engineering Science, National Cheng-Kung University, Tainan 701, Taiwan, ROC 2 Institute of Biomedical Engineering, National Cheng-Kung University, Tainan 701, Taiwan, ROC 3 Department of Logistics and Technology Management, Leader University, Tainan 709, Taiwan, ROC 4 School of Occupational Therapy, Chung Shan Medical University, Taichung 402, Taiwan, ROC 5 Faculty of Sports Medicine, Kaohsiung Medical University, Kaohsiung 807, Taiwan, ROC 6 Department of Orthopedic Surgery, Kaohsiung Medical University Hospital, Kaohsiung 807, Taiwan, ROC 7 Department of Orthopedic Surgery, Kaohsiung Municipal Hsiao-Kang Hospital, Kaohsiung 812, Taiwan, ROC Received 9 Sep 2010; Accepted 17 Nov 2010; doi: 10.5405/jmbe.844 Abstract Push-up exercises are commonly performed to strengthen the upper extremity muscles. However, the relationship between the push-up speed and upper extremity fatigue is not well understood. Accordingly, the present study investigated the effect of the push-up speed on the maximum possible number of push-up repetitions until fatigue and the upper-extremity muscle activity, respectively, in order to identify suitable push-up strategies for upper-extremity muscular strengthening. Fifteen healthy males participated in the study. Each subject performed push-ups at three different speeds (i.e., fast: 7 push-ups/10 s; regular: 5 push-ups/10 s; and slow: 4 push-ups/10 s) until fatigued. The muscle activity signals were measured during the push-up tests via surface electromyography. The strengthening effect of the push-up exercises was evaluated by measuring the myodynamic decline rate at the shoulder, elbow and wrist joints using an isokinetic dynamometer. The results showed that the maximum possible number of push-up repetitions at the fast push-up speed was around 1.34 and 1.33 times higher than that at the regular push-up speed or slow push-up speed, respectively. However, the endurance time (i.e., the time to fatigue) at the slow push-up speed was around 1.20 and 1.24 times longer than that at the fast push-up speed or regular push-up speed, respectively. Finally, at the slow push-up speed, the total muscle activations in the triceps brachii, biceps brachii, anterior deltoid, pectoralis major, and posterior deltoid, respectively, were 1.47, 2.43, 1.42, 1.48, and 1.91 times higher than those at the fast push-up speed. Therefore, the experimental results suggest that push-ups should be performed at a faster speed when the aim is to achieve a certain number of repetitions, but should be performed at a slower speed when the aim is to strengthen the upper extremity muscles. Keywords: Push-up, Upper extremity, Electromyography (EMG), Isokinetic dynamometer, Muscular strengthening 1. Introduction Push-up exercises are convenient, easily learned, and readily adapted to various levels of difficulty. As a result, they are commonly performed by health-conscious individuals and athletes to strengthen the upper extremity muscles [1]. When performing upper extremity movements, stability of the joints is ensured not only by the surrounding tissue (e.g., the ligaments and capsules), but also by the muscular contraction strength. As a result, maintaining and improving the muscular * Corresponding author: Paul Pei-Hsi Chou Tel: 886-7-3208209; Fax: 886-7-3119544 E-mail: pc.arthroscopy@gmail.com strength is essential in enhancing an individual’s performance ability and preventing movement-related injuries. Of all the training exercises available for the upper extremity, push-ups are among the most common since they yield a notable improvement in both the muscle strength and the muscle endurance. Many studies have established biomechanical kinematic and kinetic models of the upper extremity [2-6]. Furthermore, the effects of different types of push-ups on the degree of muscle activation have also been reported. For example, a narrow base position results in significantly higher electromyography (EMG) activities of the pectoralis major and triceps brachii muscle groups than a wide base position [7]. Similarly, the pectoralis major muscle activation in posterior