Home > Injury Prevention > Increasing muscle flexibility through eccentric training – a systematic literature review

Increasing muscle flexibility through eccentric training – a systematic literature review

Reference:

O’Sullivan K, McAuliffe S, DeBurca N.  The effects of eccentric training on lower limb flexibility: a systematic review.  British Journal of Sports Medicine 46(12):838-45, 2012.  doi: 10.1136/bjsports-2011-090835

http://www.ncbi.nlm.nih.gov/pubmed/22522590

What issue was addressed in the study, and why?

Lower extremity muscle flexibility is often reduced in those suffering from lower extremity musculoskeletal injury.  Static stretching is a commonly used exercise to improve muscle flexibility; however, several research studies indicate that static stretching is not effective at reducing future injury risk, post-exercise muscle soreness, or improving performance.  Thus, isolated static stretching is effective in improving flexibility; however, this does not appear to translate to reduced injury risk.

Animal based research demonstrates that eccentric training results in new sarcomeres to be created and aligned in series (sarcomerogenesis), thus facilitating greater muscle length and flexibility.  In addition, eccentric training has been shown to increase muscle force and alter the muscle’s length-tension curve by allowing peak torque to be produced at longer muscle lengths.  Due to these combined benefits (improved flexibility, peak force production, and ability to produce peak torque at longer muscle lengths), eccentric training has been proposed as an alternative method to improve muscle flexibility.  However, it is not clear if there is sufficient research from human subjects to support eccentric training as an effective method for improving lower extremity muscle flexibility.

Who were the participants in the study?

A systematic literature review was performed using the following search terms:

  • eccentric
  • strength OR training
  • flexib* OR range of motion OR fascicle

Only randomized clinical trials which compared eccentric training on measures of lower extremity muscle flexibility to either no intervention, or a different intervention, were selected for inclusion in this systematic literature.  A total of 530 potential relevant articles were retrieved.  A total of 6 articles ultimately met the inclusion criteria and were included in this review.

What did the researchers do for this study?

Two independent research assessed the methodologic quality of each included study using the PEDro scale.  Individual study quality was classified as “high” (PEDro = greater than 6 out of 10), “fair” (PEDro = between 4-5 out of 10),  or “poor” (PEDro = less than 4 out of 10) based on the study’s PEDro score.

The following lower extremity muscle groups were investigated in those studies included in the systematic literature review:

  • quadriceps (2 studies)
  • calf (2 studies)
  • hamstrings (2 studies)

Two different measures of muscle flexibility were measured in those studies included in the systematic literature review:

  • range of motion (goniometric assessment of joint motion)
  • fascicle length (diagnostic ultrasound assessment of muscle fascicle length)

What new information was learned from this study?

All 6 studies were rated as “high” quality based on their PEDro scores.  All of these studies revealed consistent evidence that eccentric training increases range of motion, or fascicle length, or both across all of the muscle groups studied.

There were a wide variety of eccentric training protocols used across the 6 studies.  A summary of the eccentric training protocols used is listed below:

  • Duration of eccentric training: 6 to 10 weeks
  • Repetitions: 6 to 10 repetitions
  • Sets: 1 to 6 sets
  • Duration of eccentric contraction: 3 to 6 seconds
  • Training load: 50 to 100% of eccentric 1 RM

Based on these findings, eccentric training is an effective means of improving lower extremity muscle flexibility, assessed by either joint range of motion or muscle fascicle length.  This finding is consistent across the different muscle groups assessed and eccentric training protocols utilized across the 6 studies included in this systematic literature review.

What are the clinical applications of this study?

The magnitude of change in muscle flexibility when performing eccentric training appears to be similar to the improvement seen when performing static stretching.  Thus, eccentric training does not appear to be more effective than static stretching.  However, given the added benefits of eccentric training (increased peak torque, ability to generate peak torque at longer muscle lengths) it may be considered a viable supplement to other forms of flexibility training.

The training duration required to achieve increased muscle flexibility following eccentric training is not clear.  The shortest duration training period was 6-weeks in the included studies.  However, animal research has shown that sarcomerogenesis begins to occur after 10 days of eccentric training.  It is also unclear how long flexibility gains are maintained after ceasing eccentric training.  Future research is needed to better investigate these aspects of eccentric training on muscle flexibility.

What are the limitations of the study, and what areas should be considered for future research?

All of the included studies utilized healthy, uninjured participants.  Thus, these findings cannot be generalized to individuals who suffer from a musculoskeletal injury.  It is known that eccentric training can facilitate increased post-exercise soreness, thus eccentric training may not be an appropriate modality for improving flexibility in those with musculoskeletal injury.

At this point in time there are no specific parameters that can be recommended for improving muscle flexibility using eccentric training.  Future research is needed to investigate the optimal training parameters (duration, repetitions, sets, eccentric contraction time, training load, frequency, etc) for improving muscle flexibility.

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Categories: Injury Prevention
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