Abstract
Background: Bilateral squat exercise is widely used in resistance training (RT) programs to increase lower limb strength and muscle mass, but this exercise does not result in significant hypertrophy of the hamstrings. It has been speculated that stretching between sets with a certain degree of tension results in muscle hypertrophy, while acute stretching could decrease performance during maximal contractions.Objective: This study investigated the acute effects of hamstring stretching before bilateral squatting on muscle thickness (MT), electromyography (EMG), and total training volume (TTV) on exercise performance.Methods: Fourteen resistance-trained young men, with ∼7.5 years of RT experience, performed the 10 repetition maximum (RM) for the barbell squat in two sessions (test–retest) separated by period after 48 h. Participants engaged in two resistance exercise conditions separated by a 1 week recovery interval: one session employed hamstrings stretching and the other did not include hamstrings stretching. Before and after each resistance exercise session, the thickness of the quadriceps muscles and biceps femoris long head were obtained by ultrasound imaging. Moreover, the EMG amplitudes for the quadriceps muscles, biceps femoris, and iliocostalis muscles were recorded during back squat performance. The TTV was also evaluated for each exercise session.Results: A significant increase in MT was observed after every set in both conditions for the evaluated quadriceps muscles (all p < 0.05), while for the biceps femoris, this effect was found only in the stretching condition (p < 0.05). EMG activity increased in the rectus femoris, vastus lateralis, and vastus medialis for the stretching condition. For the non-stretching condition, activity only increased in the vastus lateralis and medialis. There was no difference in EMG activity for the biceps femoris and iliocostalis in both conditions.Conclusion: Stretching the hamstrings immediately before each set of the back squat can be used to acutely increase biceps femoris thickness without impairing squat performance.
Highlights
Resistance training (RT) is widely recommended for subjects seeking improvements of the neuromuscular system, athletic performance, and overall health and wellness (American College of Sports Medicine, 2009; Rønnestad and Mujika, 2014; Jewiss et al, 2016; Lesinski et al, 2016; Lopez et al, 2018)
Bilateral squat exercise is widely used in resistance training (RT) programs to increase lower limb strength and muscle mass, but this exercise does not result in significant hypertrophy of the hamstrings
This study investigated the acute effects of hamstring stretching before bilateral squatting on muscle thickness (MT), electromyography (EMG), and total training volume (TTV) on exercise performance
Summary
Resistance training (RT) is widely recommended for subjects seeking improvements of the neuromuscular system, athletic performance, and overall health and wellness (American College of Sports Medicine, 2009; Rønnestad and Mujika, 2014; Jewiss et al, 2016; Lesinski et al, 2016; Lopez et al, 2018). Several studies have investigated the acute and chronic responses of agonist muscle stretching on strength, flexibility, hypertrophy, total training volume (TTV), and metabolic stress (Souza et al, 2013; Junior et al, 2017; Evangelista et al, 2019; Marin et al, 2019). Miranda et al (2015) evaluated the effect of antagonist (pectoralis major) muscle stretching, performed during the interset rest period, on seated row performance in resistance trained men. Some stretching approaches during RT may decrease muscle performance, there is a paucity of research investigating the effects of stretching the antagonist muscles on lower limb performance during squatting in trained subjects. Bilateral squat exercise is widely used in resistance training (RT) programs to increase lower limb strength and muscle mass, but this exercise does not result in significant hypertrophy of the hamstrings. It has been speculated that stretching between sets with a certain degree of tension results in muscle hypertrophy, while acute stretching could decrease performance during maximal contractions
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