Increasing muscle flexibility through eccentric training – a systematic literature review


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

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.

Categories: Injury Prevention

Is there a link between musculoskeletal injury risk and neurocognitive function?

Over the last few years research has showed an association between neurocognitive test scores and lower extremity musculoskeletal injury risk.  Specifically, decreased neurocognitive scores were observed in those individuals who had suffered lower extremity injury.  These studies have sparked discussion within the research community to better understand the potential relationship between neurocognitive function and lower extremity injury risk.  It is theorized that decreased neurocognitive function may result in poor spatial awareness, slower reaction time, and altered decision making which may facilitate an elevated injury risk.

At this point a cause and effect relationship cannot be established between neurocognitive function and lower extremity injury risk as there is still more research required to better understand this relationship.  However, the current data do suggest that neurocognitive function may be a factor to consider when assessing an individual’s overall injury risk profile.  This information should be along with other data that have also been shown to be related to injury risk, such as movement efficiency, prior injury history, and body mass index.  In addition, neurocognitive function may also be a factor to consider in the rehabilitation and  return to play decision making process, especially in cases of traumatic injury that have resulted in significant time loss.

An overview of the current research examining the relationship between neurocognitive function and musculoskeletal injury can be found at:

Categories: Uncategorized

Decreased Gluteus Maximus Activation Following Hip Joint Effusion – Presence of Arthrogenic Muscle Inhibition?


Freeman S, Mascia A, McGill S.  Arthrogenic neuromusculature inhibition: A foundational investigation of existence in the hip joint.  Clinical Biomechanics 2012 Dec 20. pii: S0268-0033(12)00271-9. doi: 10.1016/j.clinbiomech.2012.11.014. [Epub ahead of print]

What issue was addressed in the study, and why?

Arthrogenic muscle inhibition (AMI) is a reflexive inhibition of musculature surrounding a joint due to pain and/or joint effusion.  AMI results in reduced voluntary muscle activation and ultimately decreases in muscle force output.  AMI has been repeatedly shown to occur in the quadriceps muscles following knee joint injury or effusion.  It is possible that other joints and muscles may also experience AMI, similar to the knee joint and quadriceps muscles.

The gluteus maximus is theorized to be weakened and inhibited in those with lower extremity injury.   However, the neurophysiologic mechanism for this is not yet understood.  It is possible that the gluteus maximus may experience AMI in the presence of hip joint injury or effusion; however, this has not been previously investigated.  Therefore, the purpose of this study was to examine the effects of simulated hip joint effusion on voluntary gluteus maximus muscle activation.  It was theorized that the presence of hip joint effusion would cause facilitate AMI of the gluteus maximus, thereby result in decreased voluntary gluteus maximus muscle activation.

Who were the participants in the study?

A control (9 healthy participants) and intervention (12 participants who complained of hip pain and dysfunction and demonstrated findings of hip labral pathology during physical examination) group of participants were utilized in the study.

What did the researchers do for this study?

Surface EMG electrodes were attached to the gluteus maximus muscle of all subjects to measure the activation amplitude during 4 different exercises: 1) supine pelvic bridge, 2) prone hip extension, 3) active straight leg raise, 4) active hip abduction.

Both intervention and control groups were tested pre-intervention and post-intervention.  The intervention group subjects had a sterile saline solution injected into their pathologic hip joint until the point of near full capsular distension.  The control group subjects rested between test sessions and did not receive an injection.

What new information was learned from this study?

The intervention group demonstrated significantly decreased gluteus maximus activation during the supine pelvic bridge and prone hip extension exercises.  There were no such changes during the active straight leg raise and active hip abduction exercises for the intervention group.  No changes were observed in the control group between pre- and post-intervention measures of gluteus maximus activation.

Decreases in gluteus maximus activation of intervention group subjects was isolated to the side of the injection/joint effusion as there were no changes in contralateral gluteus maximus activation.  Thus, these findings indicate that voluntary activation of the gluteus maximus muscle is decreased following hip joint effusion.

What are the clinical applications of this study?

These findings extend previous research demonstrating the presence of AMI in the quadriceps muscle group following knee joint effusion and suggest a similar phenomenon occurs at the hip joint.  Decreased gluteus maximus activation following hip joint effusion may result reduced force output/strength, which may alter normal lower extremity biomechanics.  Interventions aimed to reduce AMI of the gluteus maximus following hip joint injury/effusion may be required to fully restore normal gluteal muscle function.  Research has not investigated specific interventions to combat AMI of the gluteus maximus; however, research investigating quadriceps AMI suggests that the following are important components and may be considered for treatment of gluteus maximus AMI:

  • Pain and effusion control (cryotherapy)
  • TENS (transcutaneous electrical stimulation) to stimulate spinal reflexive pathways
  • NMES (neuromuscular electrical stimulation) to stimulate inhibited muscles
  • TMS (transcranial magetic stimulation) to increase cortical motor excitability

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

Only voluntary activation of the gluteus maximus was quantified.   Previous research investigating AMI of the quadriceps utilized electrical stimulation to examine the H-reflex, which is analogous to the spinal stretch reflex.  Thus, while AMI of the gluteus maximus appears to occur following hip joint effusion, the specific neural pathways by which AMI results cannot be determined through this study.  Future research examining the specific neural pathways and mechanisms for gluteus maximus AMI post joint effusion is needed to better establish effective therapeutic interventions.

Research is needed to identify targeted interventions to combat gluteus maximus AMI.  In addition, it is important that these interventions be part of an integrated rehabilitation strategy to restore neuromuscular control and movement efficiency once gluteus maximus activation deficits have been restored.

Neuromuscular characteristics associated with knee valgus collapse during an overhead squat

Padua DA, Bell DR, Clark MA.  Neuromuscular characteristics of individuals displaying excessive medial knee displacement.  Journal of Athletic Training 47(5):525-536, 2012.

What issue was addressed in the study, and why?

Knee valgus motion is frequently hypothesized as a risk factor for multiple lower extremity injuries.  An aim of many exercise programs is to correct for excessive knee valgus motion through a variety of mobility, stability, and strengthening techniques.  The successful correction of knee valgus motion requires an understanding of the underlying neuromuscular characteristics associated with it.  Multiple theories have been proposed to explain the muscle imbalances associated with knee valgus motion; however, there is little scientific evidence to support these theories.  Identifying differences in muscle activation patterns between those who do and do not display knee valgus collapse is an initial step to validating the muscle imbalances associated with this movement dysfunction.  Therefore, the purpose of this study was to compare hip and ankle muscle activation amplitude in those with and without visual presence of knee valgus motion (medial knee displacement) during an double leg (overhead) squat task.

Who were the participants in the study?

A total of 37 participants volunteered for this study and were separated into two groups based on the presence of medial knee displacement during an double leg squat task.  The control group (CON, n=19) did not demonstrate medial knee displacement.  The medial knee displacement group (MKD, n=18) were observed to have their patella move medial to their great toe during the double leg squat, but not once a 2-inch lift was positioned under their heels.  Individuals who displayed MKD during both no-heel lift and heel-lift conditions were excluded from the study.

This was done as there are different muscle imbalances believed to be associated with knee valgus motion during no-heel-lift and heel-lift conditions.  MKD that is displayed during the no-heel-lift condition, but not during the heel-lift condition is believed to be associated with ankle muscle imbalances.  MKD that is displayed during both no-heel-lift and heel-lift conditions is thought to represent a hip muscle imbalance.  Thus, this study focused on identifying the presence of ankle muscle imbalances given the inclusion criteria.

What did the researchers do for this study?

Surface EMG electrodes were used to record the activation amplitude from the medial gastrocnemius, lateral gastrocnemius, tibialis anterior, adductor magnus, gluteus medius, and gluteus maximus muscles.  An electromagnetic motion analysis system was used to quantify medial knee displacement motion.  All variables were measured during two different double leg squat tasks performed at a controlled movement velocity and squat depth.  Subjects performed the double leg squat task during both no-heel-lift and heel-lift (2-inch) conditions.  During all double leg squat trials the individuals were instructed to keep their heels on the floor and maintain their toes pointing straight ahead.

What new information was learned from this study?

There was no difference between the CON and MKD groups for gluteus medius and gluteus maximus activation amplitude during both the no-heel-lift and heel-lift double leg squat tasks.  However, the MKD group demonstrated 34% greater activation of the adductor magnus muscle compared to the CON group.

The MKD group demonstrated greater gastrocnemius (40% greater) and tibialis anterior (25% greater) muscle activation amplitude compared to the CON group during both double leg squat tasks.

What are the clinical applications of this study?

Presence of MKD that is corrected with heel-lifts is associated with increased gastrocnemius, tibialis anterior, and adductor magnus muscle activation amplitude.  However, there was no difference in gluteal muscle activation amplitude between MKD and CON participants.  Thus, there appears to be 2 neuromuscular strategies associated with knee valgus motion.  Increased gastrocnemius and tibialis anterior activation likely increases ankle joint stiffness, thus limits the available dorsiflexion range of motion during functional tasks, which is theorized to lead to compensatory knee valgus motion.  Increased adductor magnus activation can lead to an imbalance between the gluteals and adductor muscles, resulting in a net hip adduction moment during the squat task.  In fact, the MKD participants in the current study demonstrated 4 times greater adductor magnus activation compared to their gluteal muscles, which indicates a significant muscle imbalance between these muscle groups.  This would ultimately result in the visual presence of knee valgus motion as the femur moved medially during the squat task.

Interventions aimed at inhibiting and lengthening the gastrocnemius, tibialis anterior, and adductor magnus muscles may be necessary components of exercise interventions aimed at correcting knee valgus motion.

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

All of the participants were healthy at the time of testing.  Thus, these findings are limited to healthy individuals and it is possible that different muscle activation patterns may exist in those who display knee valgus motion and are symptomatic.  Future research is needed to confirm the presence of ankle muscle imbalances (increased gastrocnemius and tibialis anterior activation) and synergistic dominance of the adductor magnus (increased adductor magnus activation) in those with MKD who are also symptomatic.

The findings from this study are part of a larger study whose findings were previously published in the following article:

Lack of Sleep and Increased Injury Risk

Recent research presented at the American Academy of Pediatrics meeting demonstrated that there was a significant relationship between the amount of nightly sleep and the likelihood of injury in a group of middle and high school aged athletes.  Specifically, there was a greater likelihood of injury associated with a lack of nightly sleep.  The press release is copied below.

This research compliments other recent research demonstrating the importance of sleep in those who are engaged in athletics and high levels of physical activity.  Previous research has shown that lack of sleep negatively impacts physical performance in athletes.  This most recent research now shows an association with lack of sleep and increased injury risk.

It is recommended that 8-10 hours of sleep are accumulated throughout the day to achieve peak recovery and avoid negative consequences on physical performance and injury risk.


Press Release:

“For the abstract, “Lack of Sleep is Associated with Increased Risk of Injury in Adolescent Athletes,” researchers asked middle and high school athletes (grades 7 to 12) enrolled at the Harvard-Westlake School in Studio City, Calif., to answer questions about the number of sports they played and the time they committed to athletics (at school and through other programs), whether they used a private coach, whether they participated in strength training, how much sleep they got on average each night, and how much they subjectively enjoyed their athletic participation. Seventy percent of the student athletes (112 out of 160 students; 54 males and 58 females; mean age 15) completed the survey, conducted in conjunction with Children’s Hospital Los Angeles. Researchers then reviewed those students’ school records pertaining to reported athletic injuries.

Hours of sleep per night was significantly associated with a decreased likelihood of injury, according to the study results. In addition, the higher the grade level of the athlete, the greater the likelihood of injury — 2.3 times greater for each additional grade in school. Gender, weeks of participating in sports per year, hours of participation per week, number of sports, strength training, private coaching and subjective assessments of “having fun in sports” were not significantly associated with injury.

“While other studies have shown that lack of sleep can affect cognitive skills and fine motor skills, nobody has really looked at this subject in terms of the adolescent athletic population,” said study author Matthew Milewski, MD.

“When we started this study, we thought the amount of sports played, year-round play, and increased specialization in sports would be much more important for injury risk,” said Dr. Milewski. Instead, “what we found is that the two most important facts were hours of sleep and grade in school.”

The advanced age risk may reflect a cumulative risk for injury after playing three or four years at the high school level, Milewski said, and older athletes are bigger, faster and stronger.”


Categories: Uncategorized

National Recovery Day – PEAKc Recovery Recommendations

The National Athletic Trainers’ Association and Gatorade have partnered to establish July 11 as National Recovery Day.

In this spirit of National Recovery Day we are posting a set of recommendations for promoting optimal recovery in athletes and physically active individuals.

The first step for recovery is to ensure movement efficiency.  Research demonstrates that a 10-15 minute dynamic warm up can effectively improve movement efficiency, enhance performance, and drastically reduce musculoskeletal injury (e.g. ACL injury rates are decreased 60-85%).  The PEAKc Dynamic Warm Up Program can help achieve these goals.  Information on the PEAKc Dynamic Warm Up Program can be found at the PEAKc website.  We recommend that this type of program be performed 3 times per week.

Another important aspect of recovery is to perform a proper cool down following training and competition.  This includes exercises to promote active recovery, muscle relaxation and lengthening, and activation of muscles prone to inhibition.  The PEAKc Recovery Program provides an overview of exercises to perform as part of a systematic and integrated recovery program.  We recommend that this type of program be performed 3 times per week.

Other vital components of recovery are proper nutrition and hydration (Re-Fuel) and rest.  An overview of recommended Re-Fuel and Rest strategies is provided in the PEAKc Refuel and Rest Strategies handout.

Regular compliance with the these recommendations for maintaining movement efficiency, re-fueling, and rest can help promote the optimal physiological environment to recover and maximize your training potential.

Train Hard, Recover Harder

Sleep Impacts Player Value in Professional Sports

Data from new research looking at the impact of daytime “sleepiness” on the careers of professional athletes was recently presented at the SLEEP 2012 conference.  These data demonstrate the impact of increased daytime “sleepiness” on a players career.  Essentially this research found that athletes who experienced higher levels of daytime “sleepiness” were less likely to remain with their team after they were drafted.  Those athletes who had low levels of daytime “sleepiness” were more likely to remain with their team in the following years after they were drafted.

These findings have two important implications.  First, it may be important to consider an athlete’s sleep habits as part of the player evaluation process when considering to draft an athlete.  These findings suggest that athletes with high daytime “sleepiness” levels are more likely to not remain with that team in the coming years after being drafted, as such they are a low value.  Conversely, athletes with better sleep habits and low daytime “sleepiness” levels are a higher value pick as they are more likely to remain with their team that drafted them.  Second, the ability to quantify the level of “sleepiness” can be easily quantified using standard survey instruments.  Thus, this is an easy assessment to incorporate into player evaluations and recovery programs to ensure they are maximizing their athletic and regeneration potential.

The bottom line is that research has repeatedly demonstrated the importance of sleep on player performance and recovery.  Thus, improving sleep behaviors should be a part of an athlete’s comprehensive recovery program to maintain performance and promote regeneration.

The press release for this study is listed below:

“Coaches, owners and fantasy-league traders take note: Sleep researcher W. Christopher Winter, MD, has uncovered a link between a pro athlete’s longevity and the degree of sleepiness experienced in the daytime.

Winter presented two studies at SLEEP 2012 that associate the career spans of baseball and football players with their voluntary answers on a sleepiness questionnaire. The results show that less sleepy football players tended to remain with their drafting NFL teams after college. In addition, attrition rates for sleepier baseball players trended higher than MLB averages.

“A team’s ability to accurately judge a prospect or a potential trade in terms of the value they will get for that player is what makes or breaks many professional sport teams,” said Winter, principal investigator of the studies and the sleep advisor for Men’s Health magazine. “These studies demonstrate that a simple evaluation of sleepiness may be a powerful tool to add to the list of tests athletes already undergo, such as the Wonderlic Cognitive Abilities Test and the 40-yard dash.”

The football study looked at 55 randomly selected college players who landed in the NFL, finding that sleepier athletes only had a 38 percent chance of staying with the team that originally drafted them. In comparison, 56 percent of the less sleepy players were considered a “value pick” because they did stay with the original team. The baseball study analyzed the sleepiness scale of 40 randomly selected baseball players and found that players who reported higher levels of daytime sleepiness also had attrition rates of 57 percent to 86 percent, well above the 30 – 35 percent MLB average.

Winter said measuring sleepiness could do more for a team than help it decide who to draft. “Addressing sleepiness in players and correcting the underlying issues causing sleepiness may help to prolong a player’s career,” he said.

Winter and his colleagues at Martha Jefferson Hospital Sleep Medicine Center and CNSM Consulting in Charlottesville, Va., used the Epworth Sleepiness Scale (ESS), a short questionnaire that can be helpful in detecting excessive daytime sleepiness. EDS is a common symptom of many sleep disorders such as obstructive sleep apnea.”

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