Article Text
PDF
Abstract
Introduction Plantar-flexor power below 50 Nm has been shown to be predictive of Achilles tendinopathy in army recruits [Mahieu, 2006]. It appears that muscle weakness may expose the tendon to greater load. As such, eccentric regimes have been proposed as an effective prophylactic intervention [Fredberg, 2008]. However, little is known about how a typical eccentric regime alters muscle power.
Aim – Investigate the effect of eccentric exercise on plantar-flexor power in healthy individuals.
Methods A test re-test study was performed with 32 healthy volunteers. Participants were assessed using a Cybex® NORM Isokinetic Dynamometer. They then completed a 12-week eccentric calf exercise programme on one leg and were re-tested [Alfredson, 1998]. The test protocol used speeds of 90°/s concentrically and 90°/s eccentrically, performed with the knee extended. Results were analysed using a paired t test (p < 0.05).
Results Significant improvements in plantar-flexor power were seen in the trained leg compared to the untrained leg following the intervention (p = 0.007). The cohort was separated into two groups depending on initial plantar-flexor power measured during the concentric 90°/s phase (Weak: <50 Nm. Strong: >50 Nm). Weak participants improved on average by 58% (p < 0.005) compared to strong participants who improved on average by 16% (p < 0.12, non-significant in eccentric peak torque).
Mean plantar-flexion average power before and after eccentric exercise (±SEM)
Discussion The results show a significant improvement in power after the intervention, with much larger gains in weaker individuals than stronger individuals. Furthermore, strong individuals did not show a significant improvement in the eccentric phase. The finding amongst stronger individuals may result from a failure to apply sufficient additional weight necessary to stimulate neuromuscular adaptation. This could explain why previous research using eccentric loading failed to change the risk of developing Achilles tendinopathy [Fredberg, 2008].
Mean plantar-flexion peak torque before and after eccentric training (± SEM)
Conclusions Eccentric loading adapts plantar-flexor muscle power, which may provide protection against Achilles tendinopathy.Improvements in plantar-flexor power associated with eccentric training depend on initial power measurements. Individuals able to generate more than 50Nm concentric force, may require additional loading to stimulate neuromuscular adaptations.
References Mahieu et al. AJSM. 2006;34:226–235
Fredberg et al. AJSM. 2008;36:451–460
Alfredson et al. AJSM. 1998;26:360–366