Abstract
Hamstrings injury is a common occurrence in athletic performance. These injuries tend to occur during a deceleration or landing task suggesting the negative work may be a key component in hamstrings injury. The purpose of this study was to investigate the muscular activity (EMG) of the biceps femoris (BF) in different phases (concentric vs. eccentric) of a Counter Movement Jump (CMJ), Squat Jump (SJ) and the Braking Phase (BP) of a landing task. Twelve female volleyball players performed 5 CMJs, SJs and BPs while surface EMG was recorded using a MuscleLab (BoscoSystemTM, Norway). EMG values were normalized to an maximal voluntary contraction. A repeated measures analysis of variance (ANOVA) was used to compare mean normalized EMG values of the concentric and eccentric portions of the CMJ with the BP and SJ. The ANOVA revealed significantly lower BF activation in the concentric and eccentric portions of the CMJ compared to the BP (64%, p < 0.001) and SJ (7%, p = 0.02), respectively. These findings suggest that the CMJ relies on a greater contribution of elastic tissues during the concentric and eccentric portions of the movement and thus requires less muscle activation of the BF.
Highlights
Most athletic movements are multi-joint in nature and require precise and powerful movement of a number of segments through a range of motion
Concentric muscle contraction is characterized by an overall shortening of the muscle length during force production (Padulo et al 2013) while eccentric muscle contractions can be described as lengthening contractions during which the overall length of the muscle becomes longer during force production (Padulo et al 2013)
The current findings demonstrate that the biphasic coupling of concentric and eccentric contractions during the stretch-shortening cycle results in significant reductions in biceps femoris (BF) muscle activation
Summary
Most athletic movements are multi-joint in nature and require precise and powerful movement of a number of segments through a range of motion. Muscular contraction is responsible for the initiation and control of segmental motions. These muscular contractions can be classified by changes in overall muscle length during force production (Bosco et al 1982a). In athletic movements it is common that a shortening contraction is performed immediately following muscle stretch, termed stretchshortening cycle (Bosco et al 1981; Padulo et al 2013). Previous research has demonstrated that more work is performed in a stretch-shortening cycle compared to a
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