Acute Effects of Practical Hamstring Stretching: Implications for Clinical Practice in the Sports Medicine Setting

Single bouts of stretching can elicit acute transient decreases in strength known as the stretching-induced force defi cit. This study examined the acute eff ects of practical stretching durations on hamstrings strength, work, and power. Forty men and women performed isokinetic leg fl exion at 60° s-1 and 180° s-1 before and after 2 minutes of stretching. Four experimental groups included static, ballistic, and proprioceptive neuromuscular facilitation (PNF) stretching, and no stretching. Peak torque, peak torque-to-body weight ratio (PTBW), total work, and average power did not change after static or PNF for the men or women. Peak torque, PTBW, and total work decreased after ballistic stretching at 180° s-1 for the men, and average power increased after ballistic stretching at 180° s-1 for the women. Despite mixed results regarding ballistic stretching, practical durations (approximately 2 minutes) of static or PNF stretching for the hamstrings may be incorporated prior to performance events to prevent stretching-induced force defi cit. [Athletic Training & Sports Health Care. 2014;6(2):59-66. ] For most physically active individuals, stretching has long been a standard part of warming up prior to athletic events or exercise.1 Stretching has been recommended because it was thought that stretching increases joint range of motion2 and decreases the risk of injury,3 although the latter has been debated.4 Muscle stretching before training and competition has been advocated as an effective injury-prevention strategy.5-7 Poor fl exibility has been highlighted as a risk factor for muscle strains8 and, more specifi cally, has been suggested as a modifi able risk factor in the prevention of hamstring muscle injury.9 Researchers believe that stretching can play a role in hamstring muscle strain prevention by improving force absorption for a given length of muscle, thereby making it more resistant to stretch injury.10 Greater fl exibility may reduce the risk of strain injury due to better compliance and ability of the passive components of the muscle–tendon unit to absorb energy.11 This improved fl exibility and compliance may reduce the incidence of hamstring muscle injuries.8,11-15 Over the past 15 years, many studies have examined the acute effects of stretching on performance,16-34 and the general outcome of these studies was that a single bout of stretching elicits acute transient decreases in strength and power.35 This observation has been termed the stretching-induced force defi cit,33 or, more broadly stated, the stretching-induced performance defi cit. Subsequently, the perception and attitude toward stretching prior to performance-based activities has shifted. Preactivity stretching has been questioned and perhaps avoided due to stretching-induced performance defi cits reported in high-quality, high-impact Drs Warren and O’Brien are from the Athletic Training Program, and Dr Smith is from the Department of Health and Human Performance, Oklahoma State University, Stillwater, and Dr Coble is from Northern Therapy and Rehabilitation, Stillwater, Oklahoma; Dr Wheeler is from the Athletic Training Program, Arkansas State University, State University, Arkansas; Dr Hetzler is from the Department of Sports Medicine and Athletic Training, Missouri State University, Springfi eld, Missouri; and Dr Cramer is from the Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, Nebraska. Received: August 19, 2013 Accepted: January 8, 2014 Posted Online: March 13, 2014 The authors have disclosed no potential confl icts of interest, fi nancial or otherwise. Address correspondence to Aric Jon Warren, EdD, ATC, CSCS, CES, Athletic Training Program, Oklahoma State University, 180 Colvin Recreation Center, Stillwater, OK 74078; e-mail: aric.warren@okstate.edu. doi:10.3928/19425864-20140306-01