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Optimal duration of stretching of the hamstring muscle group in older adults: a randomized controlled trial.

AIM
To explore the effect of variable stretching intervals on neural function and ROM.


DESIGN
Double blind randomized controlled trial.


SETTING
University research laboratory.


POPULATION
One hundred participants, 60-65 years old, with a diagnosis of tight hamstring muscles, bilaterally, were randomly assigned to either a control group or one of three intervention groups.


METHODS
Participants who were randomly placed in one of the three intervention groups, were further randomized by selection of right or left limb for intervention. Intervention groups consisted of either 15-, 30-, or 60-second stretches to hamstring muscles; whereas, the control group was given a sham stretch for 20 seconds. Main Outcome Measures included the neurophysiological outcome measures; peak to peak amplitude of somatosensory evoked potential for dermatomes L4, L5, and S1. Secondary outcome measures included knee ROM. All outcome measures were assessed before, immediately after, and 24 hours after the treatment session. Mixed linear model analysis was used to evaluate group, time, and group x time interaction effects for outcome measures.


RESULTS
Stretching for 30 & 60 seconds gave significant increase in ROM compared to control (4.64 [3.35, 5.93], 95% confidence interval; p<0.01) (10.30 [9.01, 11.6], 95% confidence interval; p<0.01) and the improvement was persistent at 24-hours' follow-up (p<0.01). However, the analysis showed significant reduction in DSSEPS's amplitudes for L4 (-1.19 [-1.35, 1.02] 95% confidence interval; p<0.01) , L5 (-1.34 [-1.56, -1.13] 95% confidence interval; p<0.01), S1 (-0.99 [-1.16 . -.83] 95% confidence interval; p<0.01) after 60-second static Hamstring muscle stretch. The reduction was persistent at 24-hours' follow-up (p<0.01).


CONCLUSIONS
Stretching hamstring for 30 seconds was optimal in increasing the knee range of motion and minimizing the negative effects on the neural function of the involved nerve roots. Thus, 60-second static hamstring muscle stretching, places increased stress and strain on the nervous system and should be avoided.


CLINICAL REHABILITATION IMPACT
It is well established that stretching is an effective intervention to treat many neuromuscular and musculoskeletal problems. However, which exact parameters to follow during stretching procedures remains controversial. Our findings indicate that 60-second static stretching of hamstring at end ranges of motion, likely place increased stress and strain on the nerve roots and central nervous syste.