E. D. RYAN, T. J. HERDA, P. B. COSTA, A. A. WALTER, K. M. HOGE, AND J. T. CRAMER
Applied Musculoskeletal and Physiology Laboratory, Oklahoma State University, Stillwater, OK; and Biophysics Laboratory, University of Oklahoma, Norman, OK
Many previous studies have reported a temporary decrease in muscle strength following an acute bout of stretching, which has been termed the ‘‘stretching-induced force deficit.’’ However, chronic stretching programs have reported mixed results demonstrating improvements or no changes in performance.
This particular study examined the effects of chronic stretch training of the plantar flexors on muscle strength at multiple joint angles.
Stretch Training & Muscle Strength
Thirty-one healthy men volunteered for this investigation and were randomly assigned to either a stretch training group or a control group for four weeks. At baseline (week 1) and post-testing (week 5) all subjects completed isometric maximal voluntary contractions (MVCs) at -19 degrees, -9 degrees, 1 degrees, and 12 degrees of dorsiflexion (0 degrees = neutral ankle joint angle). Testing was performed on a custom-built load cell apparatus attached to a calibrated isokinetic dynamometer. For the MVC assessments, subjects were instructed to provide maximal force of the plantar flexors for 4 seconds at each randomly ordered joint angle.
The stretch training protocol included four 135 second passive stretches (9 min of time under stretch) performed 3 times per week which was held at each subject’s maximum tolerable passive stretching torque (the point of discomfort). Five to 10 seconds was allowed between each stretching repetition.
There was a 14% increase in plantar flexor MVC strength for the STRETCH group and no change for the CONTROL group from weeks 1 – 5 across all joint angles.
These findings suggested that chronic stretch training results in increases in muscle strength at all the joint angles tested. In addition, the stretch training protocol did not alter the joint angle at which peak isometric strength was produced. These findings may be useful for coaches or other professionals who are interested in incorporating passive stretching routines into their training programs. It appears 9 min of passive stretching performed 3 times a week for 4 weeks results in significant (14%) gains in muscle strength.