Abstract
Background: The effects of proprioceptive neuromuscular facilitation (PNF) stretching on muscle imbalance are not fully understood. The aim of this study was to examine the acute effects of PNF stretching on knee extension and flexion peak torque (PT), as well as the conventional and functional hamstrings to quadriceps (H:Q) ratios. Methods: Fifteen men (age = 22 ± 1 years; body mass = 76 ± 12 kg; height = 176 ± 7 cm) and fifteen women (age = 22 ± 2 years; body mass = 63 ± 8 kg; height = 161 ± 5 cm) performed concentric quadriceps and hamstrings, and eccentric hamstrings muscle actions at different angular velocities (60, 180, and 300°·s−1 concentric; 60 and 180°·s−1 eccentric) before and after a bout of PNF stretching, and a control condition. Results: Neither PNF or control conditions affected concentric PT or H:Q ratios (p > 0.05), apart from knee extension at 60°·s−1 in men (p = 0.001). However, there was a reduction in hamstrings eccentric PT in both control and PNF conditions for men and women (p = 0.003). Conclusions: PNF stretching of the hamstrings may not adversely affect the H:Q ratios, and consequently not negatively affect injury risk associated with muscular strength imbalances.
Highlights
Stretching has been typically recommended as part of athletic and recreational pre-performance activities and warm-up [1,2,3]
Dynamic stretching has been suggested to lead to changes in neural factors such as greater electromechanical delay resulting from the increased slack in the musculotendinous unit, reducing force direct transmittal from the muscle to the bone [11]
These findings suggest proprioceptive neuromuscular facilitation (PNF) stretching of the hamstrings may not adversely affect the H:Q ratios, and not negatively affect injury risk associated with muscular strength imbalances
Summary
Stretching has been typically recommended as part of athletic and recreational pre-performance activities and warm-up [1,2,3]. Recent evidence has shown both DS and SS may cause adverse effects on performance and might even increase injury risk if performed immediately prior to exercise and sport events [10,11,12,13]. This occurs because stretching may lead to alterations in neural factors and/or the mechanical components of the skeletal muscle contraction, compromising strength and affecting muscle imbalance [11,12]. Conclusions: PNF stretching of the hamstrings may not adversely affect the H:Q ratios, and not negatively affect injury risk associated with muscular strength imbalances
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