Exercise Type, Elbow Angle Effects During the Push-up Plus
Exercise Type, Elbow Angle Effects During the Push-up Plus
Proper positioning of the scapula during upper extremity movement is crucial for the maintenance of joint function and health, optimal muscle lengths, force production, and bony and soft tissue alignment. This positioning is afforded by the coordinated actions of muscles that both anchor the scapula to the trunk, and work to rotate it in three dimensions during dynamic movements. Substantial research has focused on the normal motions of the scapula and corresponding actions of healthy stabilizing muscles during movement, as well as how these characteristics differ with acute and chronic injury. In a healthy shoulder, overhead motion involves rotation of the scapula in such a way that soft tissues in the subacromial space are not impinged upon. In the case of many acute and chronic injuries, authors have consistently reported positioning of the scapula that increases the impingement of soft tissues, and results in pain. For this reason, one of the chief objectives in the rehabilitation of shoulder injuries is re-establishing proper scapular positioning during movement. This is often done using several variants of the push-up exercise. The push-up plus (PUP) exercise, a commonly prescribed push-up variant to target scapular muscle stabilizers, is characterized by a standard push-up motion with a protraction of the scapula upon completion of the push-up repetition. Additionally, the PUP has been shown to result in substantial activation of the scapular stabilizer muscle.
Many authors have reported that the forces encountered and the activation levels of muscles primarily involved in many push-up variants increase with the intensity of the push-up exercise (i.e., on knees, traditional push-up, feet on exercise ball, slings), while the activation of the scapular stabilizing muscles seems to depend on a combination of the weight-bearing demand and degree of arm elevation during the movement. Both traditional and modified push-up plus variants have been shown to elicit greater activation of the serratus anterior muscle compared to that of the upper trapezius. In fact, Decker et al. reported that SA activation in the modified push-up plus was equivalent to that in the traditional variant, with a lower arm elevation and, even with the lower weight-bearing demand. However, the wall push-up elicited a high upper trapezius/serratus anterior ratio. The literature suggests that proper activation of the stabilizing musculature is a major contributor to optimal performance during upper extremity movements, and helps to prevent excessive stresses on associated soft tissues. Therefore, prevention and treatment of shoulder injuries has traditionally included the prescription of many variations of the push-up exercise. Although a substantial body of research is available regarding muscle activation levels during various push-up exercises, these studies have used only static postures or differences in the overall muscle activity, and have not incorporated measures of the forces required, in order to support and accelerate the body weight. Similarly, studies examining force output during these variants have focused either on peak and/or average forces across the range of motion (ROM) during a dynamic motion or forces exerted at discrete positions within the ROM. These are two areas that need further study, given that muscle lengths and external torques are altered throughout the push-up ROM, leading to changes in scapular kinematics. As a result, the purpose of this study was to examine the effect of push-up plus variant type (traditional vs. modified) and elbow position (5° increments across the range of motion from 100° to full extension) on electromyographical activity of four stabilizer muscles (upper trapezius, lower trapezius, serratus anterior, and infraspinatus) and vertical ground reaction force during concentric phase of the motion. We hypothesized that the traditional PUP would result in higher EMG activity and vertical ground reaction forces compared to the modified PUP.
Background
Proper positioning of the scapula during upper extremity movement is crucial for the maintenance of joint function and health, optimal muscle lengths, force production, and bony and soft tissue alignment. This positioning is afforded by the coordinated actions of muscles that both anchor the scapula to the trunk, and work to rotate it in three dimensions during dynamic movements. Substantial research has focused on the normal motions of the scapula and corresponding actions of healthy stabilizing muscles during movement, as well as how these characteristics differ with acute and chronic injury. In a healthy shoulder, overhead motion involves rotation of the scapula in such a way that soft tissues in the subacromial space are not impinged upon. In the case of many acute and chronic injuries, authors have consistently reported positioning of the scapula that increases the impingement of soft tissues, and results in pain. For this reason, one of the chief objectives in the rehabilitation of shoulder injuries is re-establishing proper scapular positioning during movement. This is often done using several variants of the push-up exercise. The push-up plus (PUP) exercise, a commonly prescribed push-up variant to target scapular muscle stabilizers, is characterized by a standard push-up motion with a protraction of the scapula upon completion of the push-up repetition. Additionally, the PUP has been shown to result in substantial activation of the scapular stabilizer muscle.
Many authors have reported that the forces encountered and the activation levels of muscles primarily involved in many push-up variants increase with the intensity of the push-up exercise (i.e., on knees, traditional push-up, feet on exercise ball, slings), while the activation of the scapular stabilizing muscles seems to depend on a combination of the weight-bearing demand and degree of arm elevation during the movement. Both traditional and modified push-up plus variants have been shown to elicit greater activation of the serratus anterior muscle compared to that of the upper trapezius. In fact, Decker et al. reported that SA activation in the modified push-up plus was equivalent to that in the traditional variant, with a lower arm elevation and, even with the lower weight-bearing demand. However, the wall push-up elicited a high upper trapezius/serratus anterior ratio. The literature suggests that proper activation of the stabilizing musculature is a major contributor to optimal performance during upper extremity movements, and helps to prevent excessive stresses on associated soft tissues. Therefore, prevention and treatment of shoulder injuries has traditionally included the prescription of many variations of the push-up exercise. Although a substantial body of research is available regarding muscle activation levels during various push-up exercises, these studies have used only static postures or differences in the overall muscle activity, and have not incorporated measures of the forces required, in order to support and accelerate the body weight. Similarly, studies examining force output during these variants have focused either on peak and/or average forces across the range of motion (ROM) during a dynamic motion or forces exerted at discrete positions within the ROM. These are two areas that need further study, given that muscle lengths and external torques are altered throughout the push-up ROM, leading to changes in scapular kinematics. As a result, the purpose of this study was to examine the effect of push-up plus variant type (traditional vs. modified) and elbow position (5° increments across the range of motion from 100° to full extension) on electromyographical activity of four stabilizer muscles (upper trapezius, lower trapezius, serratus anterior, and infraspinatus) and vertical ground reaction force during concentric phase of the motion. We hypothesized that the traditional PUP would result in higher EMG activity and vertical ground reaction forces compared to the modified PUP.
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