Meeting Abstract

98.4  Wednesday, Jan. 7  Fatigue fiddles with fowl function: Altered muscle function during locomotion HIGHAM, T.E.*; BIEWENER, A.A.; Clemson University; Harvard University thigham@clemson.edu

For over a century, scientists have been captivated and challenged by the mechanisms and effects of muscle fatigue, which is defined as a reduction in muscle force as a consequence of exercise. Because muscle force is important for executing a behavior with maximum performance, fatigue likely has important implications for fitness. Although much is known about whole-limb force generation and muscle activation patterns in relation to fatigue under controlled conditions, we know little about the effects of whole-body fatigue on the in vivo dynamics of limb muscles. Following fatiguing exercise (5-8 min) on an inclined treadmill at 2.0 m/s, we show here that limb kinematics and contractile function in the lateral (LG) and medial (MG) gastrocnemius of helmeted guinea fowl (Numida meleagris) are significantly altered during subsequent steady running at 2 m/s on a level treadmill. Stride frequency was significantly lower in the fatigued trials (2.80.04 Hz) compared with the non-fatigued trials (3.10.03 Hz), and this was correlated with a decrease in mean EMG frequency. Related to this was a decrease in the time to peak force for both the LG and MG with fatigue, suggesting selective fatigue of the fast-twitch fibers. Variation in peak force measured directly from the muscles distal tendons increased significantly with fatigue, suggesting that locomotor stability might be compromised. Negative work increased in all muscles and regions with fatigue, revealing the dynamic changes that can occur within muscles during fatigue. Fascicle shortening in the proximal MG, but not the distal MG, decreased significantly with fatigue. This is surprising given that these two synergists are often thought to function uniformly. This work was funded by an NIH grant (R01-AR047679).