Fast muscle function in the European eel (Anguilla anguilla L.) during aquatic and terrestrial locomotion

Eels are capable of locomotion both in water and on land using undulations of the body axis. Axial undulations are powered by the lateral musculature. Differences in kinematics and the underlying patterns of fast muscle activation are apparent between locomotion in these two environments. The change in isometric fast muscle properties with axial location was less marked than in most other species. Time from stimulus to peak force (T(a)) did not change significantly with axial position and was 82+/-6 ms at 0.45BL and 93+/-3 ms at 0.75BL, where BL is total body length. Time from stimulus to 90% relaxation (T(90)) changed significantly with axial location, increasing from 203+/-11ms at 0.45BL to 239+/-9 ms at 0.75BL. Fast muscle power outputs were measured using the work loop technique. Maximum power outputs at +/-5% strain using optimal stimuli were 17.3+/-1.3W kg(-1) in muscle from 0.45BL and 16.3+/-1.5W kg(-1) in muscle from 0.75BL. Power output peaked at a cycle frequency of 2Hz. The stimulus patterns associated with swimming generated greater force and power than those associated with terrestrial crawling. This decrease in muscle performance in eels may occur because on land the eel is constrained to a particular kinematic pattern in order to produce thrust against an underlying substratum.