A comprehensive assessment of the cross-training effect in ankle dorsiflexors of healthy subjects: A randomized controlled study

- A crossed transfer of peak torque and work is reported in ankle dorsiflexor muscles.
- Work increased more than peak torque, depending on the angular velocity employed.
- Performance gains were significantly larger in the untrained than trained muscles.
- Peak torque and work contribute in a different proportion to muscle strength.
- Analysis of peak torque, work and their ratio allows a full assessment of strength.

PurposeTo investigate the cross-training effect, induced on ankle dorsiflexors (AD) by unilateral strength-training of the contralateral muscles, as transfer of peak torque (PT) and muscle work (MW) and their relative contributions to muscle performance.MethodsThirty healthy volunteers were randomly assigned to a training or control group. The trained group sustained a 4-week maximal isokinetic training of the stronger AD at 90 and 45°/s. At both angular velocities, PT, MW and MW/PT ratio were measured from both legs at baseline and after intervention (trained group) or no-intervention (controls). The familiarization/learning-effect was calculated and subtracted by PT and MW measures to obtain their net changes.ResultsNet PT increased in both legs (untrained: +27.5% at 90°/s and +17.9% at 45°/s; trained: +15% at 90°/s and +16.3% at 45°/s). Similarly, net MW increased in both the untrained (90°/s: +29.6%; 45°/s: +37%) and trained (90°/s: +23.4%; 45°/s: +18.3%) legs. PT and MW gains were larger in the untrained than trained AD (p < 0.0005), with MW improving more than PT at 45°/s (p = 0.04). The MW/PT ratio increased bilaterally only in the trained group (p < 0.05), depending on the angular velocity.ConclusionsThe cross-training effect occurred in AD muscles in terms of both PT and MW, with MW adding valuable information to PT-analysis in describing muscle performance. Moreover, the MW/PT ratio allowed estimating the contributions of these parameters to muscle capability and may represent a novel index in isokinetic testing. The greater improvements in the untrained than trained limb raises interesting clinical implications in asymmetric conditions.