Does Cross-Training balance strength asymmetry in healthy subjects? A proof-of-concept trial

Question
We wondered whether an unconventional intervention, the Cross-Training, could improve the performance
of dorsiflexor muscles in an inveterate iatrogenic drop-foot. We investigated whether unilateral, maximal
isokinetic training of the normal leg would induce, in the contralateral affected side, a worthy strengthtransfer,
with cortico-spinal and gait adaptations.
Methods
A 59-year-old man who suffered in childhood a surgical-induced damage of the left common peroneal
nerve at the head of the fibula, performed a 4-week training (16 sessions) of the normal leg, at 40°/sangular
velocity. Before and after training, the subject underwent a test-retest assessment procedure
including: 1) bilateral isokinetic dynamometry of the dorsiflexors’ performance; 2) stance and gait-analysis;
3) recording of cortical and spinal drives to the affected leg, through measurement of central motor
conduction time, input-output curve, cortical silent period (cSP), SICI, ICF, SICF, H-reflex, V-wave and Mwave.
Results
The untrained-affected dorsiflexors showed considerable increases in strength (peak-torque: pre=23N/m;
post=31N/m), power (pre=14W; post=22W) and total-work (pre=9J; post=22J). Ankle dorsiflexion increased
from 4 to 11 degrees. Overall gait pattern was unchanged, however a better stance performance was
suggested by changes in heel-to-forefoot contact-time % of stance-time (pre=0.5%; post=3.4%) and mean
step-length (pre=30cm; post=34cm). An increase in cortico-spinal drive to the untrained-affected leg was
revealed only by reduction of cSP duration (120%RMT: pre=154ms; post=144ms; 150%RMT: pre=196ms;
post=182ms).
Conclusions
Maximal isokinetic cross-training induced considerable improvements in the performance of the untrainedaffected
leg with a parallel increase in its cortico-spinal drive. In this report cross-training was a viable and
effective rehabilitative approach to drop-foot.