Physical training is associated with changes in nuclear magnetic resonance and morphometrical parameters of the skeletal muscle in senescent mice.

The effect of a three-month training period on T2 relaxation time as well as on myofibre size and type was investigated in the lower limbs of senescent mice. After training, T2 (which is a magnetic resonance imaging parameter known to increase during acute exercise) was significantly higher in trained mice (36.37+/-1.27 vs 37.76+/-2.06 ms, p=0.003, n=8), whereas no change was found in non-trained animals (36.35+/-1.02 vs 36.24+/-1.15 ms, p=0.278, n=8). The percentage of muscle limb area evaluated in vivo on magnetic resonance images before and after the experimental period was unchanged in trained mice (69.84+/-2.50 vs 70.29+/-2.29, p=0.896, n=3) and decreased in non-trained animals (72.98+/-1.68 vs 64.62+/-2.34, p=0.006, n=3). Cross-sectional area of fast and slow myofibres, evaluated on paraffin-embedded samples after immunolabelling for skeletal fast fibre myosin, was lower in non-trained than in trained mice in both gastrocnemius and quadriceps muscle, but no change in slow/fast fibre ratio nor in apoptotic rate was found. These data show that training can prevent sarcopenia in senescent mice by affecting muscle status and inducing myofibre hypertrophy in the absence of significant muscle damage.