Research Review By Kevin Neeld©

Date Posted:

October 2009

Study Title:

The Time Course of Musculotendinous Stiffness Responses Following Different Durations of Passive Stretching

Authors:

Ryan ED et al.

Author's Affiliations:

Department of Health and Exercise Science, University of Oklahoma, Norman, OK; New York Obesity Research Center, College of Physicians and Surgeons Body Composition, Columbia University, New York, NY; Department of Exercise Science and Health Promotion, Florida Atlantic University, Davie, FL

Publication Information:

Journal of Orthopaedic and Sports Physical Therapy 2008; 38(10): 632-639.

Background Information:

Within and outside of athletics, stretching prior to activity has become commonplace as a proposed strategy to minimize injury risk. In the last decade, this relationship between pre-activity stretching and injury reduction has been challenged, with some authors even hypothesizing that pre-activity stretching may increase injury risk.

While improvements in joint range of motion (ROM) are typically used to assess the efficacy of stretching, musculotendinous stiffness (MTS) may better describe how the muscle-tendon unit is able to absorb and reduce force. MTS is assessed by measuring the joint angle-specific torque generated during a passive stretch. Theoretically, MTS (assessed by passive torque) will be reduced at any given joint angle following stretching.

The dose-response relationship of stretching and MTS remains poorly described. Previous authors have reported a decrease in MTS following stretching, but only when the stretching lasted a staggeringly unpractical 2.5 - 30 minutes. While this research provides valuable insight into alterations in muscle and soft-tissue property following prolonged changes in body position (which could be applied to prolonged postures such as sitting at a desk at work or sleeping at night), application to pre-competition or training routines is limited.

The purpose of this study was to assess how MTS is affected immediately following and up to 30 minutes after stretching bouts of practical durations (2-8 minutes).

Pertinent Results:

  • For all stretching conditions (2-minute, 4-minute, and 8-minute – see below), MTS was significantly reduced immediately following the bout of stretching (p < 0.05).
  • For the 2-minute stretching bout, MTS fully recovered to pre-stretching levels within 10 minutes.
  • For the 4-minute and 8-minute stretching bouts, MTS fully recovered to pre-stretching levels within 20 minutes.
  • Average surface EMG amplitude for medial gastrocnemius and soleus were 0.28% MVC and 0.18% MVC, respectively. There were no significant changes in surface EMG taken from the medial gastrocnemius or soleus during any of the time points under any conditions.

Clinical Application & Conclusions:

The primary finding of this study is that MTS was significantly reduced immediately following all the stretching bouts. A secondary finding is that MTS fully recovered within 20 minutes for all conditions.

Because pre-competition stretching routines usually occur well in advance of the 20 minutes preceding activity, an argument can be made that stretching will not result in any reduction in injury risk due to a decrease in MTS. Another logical conclusion, although not discussed in the current study, is that reported decrease in joint torque, power, and balance immediately following stretching, which could result secondary to decreases in MTS, may also return to baseline levels within 20 minutes.

Research noting decreases in various performance measures has led to an industry-wide boycott of stretching altogether. Because these studies assess performance measures immediately following stretching, which is not how stretching is used “in the field”, the real-world application of these studies is minimal. Stretching should be included as part of a comprehensive training or wellness program. In an athletic setting, it may be best to stretch before the training session, as this is when the athletes are the most rested and focused.

Study Methods:

Participants included seven male (average age: 24 years; height: 178 cm; body mass: 82 kg) and five female (average age: 21; height: 157 cm; body mass: 56 kg) recreationally active college students. During a familiarization trial, individual participant maximal tolerable torque threshold was determined during end range plantarflexion using a Biodex isokinetic dynamometer.

Testing consisted of the Biodex moving the each participant’s ankle into plantar flexion at 5°/s until their individual maximal tolerable torque was reached. At this point, the stretch was held at a constant torque for a 30s bout, followed by a 20s rest period.

The cycle was repeated until the total desired stretch time (e.g. 2, 4, or 8 minutes) was reached. For consistency among trials, passive torque was assessed at four different joint angles for each trial. Surface EMG amplitude of the medial gastrocnemius and soleus was calculated in 200ms (the equivalent of 1° of joint motion) bins.

Study Strengths / Weaknesses:

The study had a few notable limitations:
  • The sample size was relatively small and consisted of only recreationally active young participants. Although likely, it remains to be verified that these results apply to individuals of different ages and activity levels.
  • Only the passive tension of the plantar flexors were assessed in the current study. While this muscle group is of great importance to functional activity, it is unclear whether the results of this study are applicable to other important musculature (e.g. the quadriceps or hamstrings).
  • This study assessed passive resistance to movement. During activity, it is more likely that muscular force production involves a combination of active and passive efforts. For example, the plantar flexors are contracting eccentrically while dorsiflexing during running. The total force output will be a combination of the eccentric force production of the involved musculature, as well as the passive force production. This study does not provide insight into changes in the neural drive to the muscle, nor the mechanical properties of the muscle pertaining to active muscle contraction. As a result, caution should be taken when making broad training conclusions using the findings of this study.

Additional References:

  1. Fowles JR et al. Reduced strength after passive stretch of the human plantarflexors. J Appl Physiol, 2000, 89, 1179-1188.
  2. Magnusson SP et al. Biomechanical responses to repeated stretches in human hamstring muscle in vivo. Am J Sports Med, 1996, 24: 622-628.
  3. Morse CI et al. The acute effect of stretching on the passive stiffness of the human gastrocnemius muscle tendon unit. J Physiol, 2008, 586: 97-106.