Research update 4.06.12

The role of neuromuscular inhibition in hamstring strain injury recurrence

Conclusion: Current evidence indicates that athletes return to competition after hamstring injury having developed maladaptations that predispose them to further injury.These maladaptations include eccentric hamstring weakness, selective hamstring atrophy and shifts in the knee flexor torque-joint angle relationship.  When rehabilitating athletes to return to competition following hamstring strain injury, the role of neuromuscular inhibition in re-injury should be considered.

Terminology and classification of muscle injuries in sport: The Munich consensus statement

Conclusions: This consensus statement aims to standardise the definitions and terms of muscle disorders and injuries and proposes a practical and comprehensive classification. Functional muscle disorders are differentiated from structural injuries. The use of the term strain—if used undifferentiated—is no longer recommended, since it is a biomechanical term, not well defined and used indiscriminately for anatomically and functionally different muscle injuries. Instead of this, we propose to use the term tear for structural injuries, graded into (minor and moderate) partial and (sub)total tears, used only for muscle injuries with macroscopic evidence of muscle damage (structural injuries). While this classification is most applicable to lower limb muscle injuries, it can be translated also to the upper limb.

Commentary: if you are tired of, or confused by terms like muscle strain, pulled muscle or hardened muscle, this excellent paper will help you out!

Update on the female athlete triad

Current literature highlights new assessments, such as measurements of bone microarchitecture and hormone levels to better evaluate bone strength and the hormonal and metabolic profile of athletes with and at risk for the Triad. Recent data also provides support for additional potential consequences of the Triad, such as endothelial dysfunction and related cardiovascular effects, stress fractures, and musculoskeletal injuries. Additional prospective research is needed to evaluate long-term indicators and consequences of the Triad and identify effective behavioral treatment strategies.

Commentary: this is an important update on the issues of the female athlete triad, and broadens our understanding of the consequences of this condition to include both cardiovascular and musculoskeletal events.

Minimalist shoe injuries: Three case reports

Three injuries from runners who immediately transitioned to minimalist footwear is hardly a surprise and hardly representative of the minimalist discussion. It does however underline the need to caution all athletes wanting to experiment with minimalist footwear.

The injuries sustained were 2 cases of achilles tendinopathy and one of a stress fracture to the 3rd metatarsal.

The shoes presumably involved in the injury process were not identified.

EMG and tibial shock upon the first attempt at barefoot running

Conclusion: Based on our data, the initial change in mechanics may have detrimental effects on the runner. While it has been argued that BTS 9midfoot or forefoot strike) running may ultimately be less injurious, these data indicate that habitually SHS (heel strikers) runners who choose to transition into a BTS (midfoot or forefoot strike) technique must undertake the process cautiously.

Commentary: the results were actually a little more damning than the somewhat meek conclusion above. This study found, that compared to barefoot heel striking, striking with a mid or foreffot pattern: 

1. significantly increased the average EMG of the medial gastrocnemius (p = .05),
2. significantly increased the average and peak tibial shock (p < .01),
3. and significantly increased the minimum knee flexion angle (p < .01). 

This study evaluated the effects of the initial transition from shod to barefoot running on tibial shock and muscle activation. It was found that peak shock and average shock were higher in the barefoot conditions, suggesting that stress injuries are more likely to occur while running barefoot during the early stages of the transition. It was also found that the average MG muscle activity was greater in the barefoot conditions than in the SHS condition, while the peak EMG was similar, which suggests that the plantar flexor muscles are firing in longer, less efficient bursts, increasing the likelihood of fatigue. Barefoot running also resulted in a more flexed knee at touchdown, which indicates that muscle activity is likely to be greater in the thigh during barefoot running. 

None of this suggests barefoot running, and the presumed change to a forefoot strike pattern, is protective of injury.

The Effects of Wedged Footwear on Lower Limb Frontal Plane Biomechanics During Running 

Lewinson, Ryan T.  Fukuchi, Claudiane A. BSc,  Worobets, Jay T.  Stefanyshyn, Darren J.  Clinical Journal of Sport Medicine Issue: Volume 23(3), May 2013, p 208–215

Abstract

Objective: Patellofemoral pain syndrome (PFPS), the most common running injury, has been associated with increased internal knee abduction angular impulses (KAAI). Wedged footwear can reduce these impulses during walking, but their effects during running are not well understood. The purpose of this study was to identify the effects of wedged footwear on KAAIs and describe the mechanism by which wedged footwear alters KAAIs during running.

Design: Controlled laboratory study.

Participants: Nine healthy male subjects.

Interventions: Participants ran at a speed of 4 m/s with 7 different footwear conditions (3-, 6-, and 9-mm lateral wedges; 3-, 6-, and 9-mm medial wedges; neutral).

Main Outcome Measures: Knee abduction angular impulses and 8 predictor variables were measured and compared by 1-way repeated measures analysis of variance ([alpha] = 0.05) with Bonferroni-adjusted 2-tailed paired t tests for post hoc analysis ([alpha] = 0.002). Correlation ([alpha] = 0.05) was used to determine the relationship between the mediolateral center of pressure to ankle joint center (COP-AJC) lever arm length and KAAIs.

Results: Laterally wedged conditions produced significantly lower KAAIs (P = 0.001) than medial wedge conditions. Peak knee abduction moments decreased (P = 0.001), whereas ankle inversion moments (P = 0.041) and the COP-AJC lever arms increased (P < 0.001) as wedges progressed from medial to lateral. KAAIs were negatively correlated with COP-AJC lever arm length (r = -0.50, P < 0.001).

Conclusions: KAAIs are reduced with laterally wedged footwear because of lateral shifts in the center of pressure beneath the foot, which then increases ankle inversion moments and decreases peak knee abduction moments. Laterally wedged footwear may therefore offer greater relief to runners with PFPS than medially wedged footwear by reducing KAAIs.

Commentary: A small study from the revered Human Performance Laboratory in Calgary (home to Benno Nigg) nevertheless is food for thought in terms of the management of patellofemoral pain. This study indicated the use of laterally (valgus) wedged footwear may be beneficial for runners suffering PFPS. The increased ankle inversion moment does need to be kept in mind however.

Medially posted insoles consistently influence foot pronation in runners with and without anterior knee pain

Commentary: I urge you to read this excellent paper from Joe Hamill's group at UMass. Several unique design features distinguish this study from any other undertaken, all of which were designed to standardise the testing protocols.

The reslults, in terms of using a simple shoe insole with a 4 degree medial posting were unequivocal and stunning.

It was hypothesized that medially posted insoles would reduce eversion, eversion velocity, tibial internal rotation, and knee internal rotation in runners with and without AKP. This study provides strong evidence for the foot related hypotheses, with a majority of runners, regardless of injury status, moving in the predicted direction of reduced eversion and eversion velocity. On the contrary, it did not support the hypothesis for the tibia and knee. While some evidence was present that insoles could delay peak tibial internal rotation, they were found to increase transverse knee ROM and demonstrated a trend toward increasing peak knee internal rotation.