Coordinated changes of kinematics and muscle fibre properties with prolonged endurance training

The objective of this study was to investigate the relationship between kinematic variables and muscle characteristics by determining (1) if heavy endurance training alters these variables and (2) if such modifications occur in a coordinated manner. Fifteen Andalusian stallions age 41-45 months were used. Five horses were used as controls and 10 horses underwent a training programme based on aerobic exercise for 8 months. Intensity of exercise was adjusted individually for each horse according to a standardised exercise test. Stride kinematic characteristics at the trot were analysed by videography and gluteus medius muscle biopsies were removed before and after the experiment. Muscle samples were analysed immunohistochemically for fibre types and fibre sizes. After training, stride frequency increased (6%, P < 0.05), whereas stride duration and stance time of the stride decreased (6 and 10% respectively, P < 0.05 in both). The percentage of type IIA fibres increased (25%, P < 0.01), whereas the percentage of type IIX fibres decreased (80%, P < 0.001). Training had no significant effect on the percentage of types IIAX and I fibres. After training, mean lesser fibre diameters of types I and IIA fibres increased (13 and 10%, respectively; P < 0.05). These results suggest that prolonged endurance training alters kinematic and muscle fibre properties in a coordinated manner, reflecting a greater stability and more efficient propulsion associated with an increase in muscle fatigue resistance and strength. This adaptive response has an impact on athletic performance.