Abstract
To study the effects of muscle fiber distribution (m. vastus lateralis) on the mechanical
efficiency of human locomotion, 12 subjects were observed, six in the slow-twitch
(ST) group (38.0% ± 6.1% FT) and six in the fast-twitch (FT) group (63.8% ± 5.9% FT).
Pure positive, pure negative, and a combination of negative and positive work were
performed with a special “sledge ergometer.” The mechanical efficiency of the pure
positive work (η) was on the average 16.4% ± 2.5% and 17.1% ± 2.1% for the ST and
FT groups, respectively. The mechanical efficiency of the pure negative work (η) was
slightly greater in the ST group (94.0% ± 30.2% vs 79.6% ± 32.7%, P = NS). The mechanical efficiency of the positive work in the combined negative/positive
work (η+) was on the average in the ST group 36.4% ± 5.9% and in the FT group 33.2% ± 5.5%
(t = 2.02, P < 0.05). The η+ and the calculated elastic parameters (work due to elasticity Wel, utilization of
the prestretch %EI, and relative Wel) together with the EMG analysis demonstrated
that the ST group had a better stiffness regulation and elastic performance. It is
suggested that the basic differences in the reflex control between the two types of
muscles and functional differences between the respective fiber types could be the
possible reasons for the results observed under the conditions of the present slow-type
stretch-shortening cycle exercises.
Key words
mechanical efficiency - muscle fiber distribution - positive work - negative work
- elastic characteristics
