Metabolic cost of lengthening, isometric and shortening contractions in maximally stimulated rat skeletal muscle.
ACTA ACUST UNITED AC 2005;
182:179-87. [PMID:
15450114 DOI:
10.1111/j.1365-201x.2004.01338.x]
[Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
AIM
The present study investigated the energy cost of lengthening, isometric and shortening contractions in rat muscle (n = 19).
METHODS
With electrical stimulation the rat medial gastrocnemius muscle was maximally stimulated to perform 10 lengthening, isometric and shortening contractions (velocity 25 mm s(-1)) under experimental conditions (e.g. temperature, movement velocity) that resemble conditions in human movement.
RESULTS
Mean +/- SD force-time-integral of the first contraction was significantly different between the three protocols, 2.4 +/- 0.2, 1.7 +/- 0.2 and 1.0 +/- 0.2 N s, respectively (P < 0.05). High-energy phosphate consumption was not significantly different between the three modes of exercise but a trend could be observed from lengthening (7.7 +/- 2.7 micromol approximately P muscle(-1)) to isometric (8.9 +/- 2.2 micromol approximately P muscle(-1)) to shortening contractions (10.4 +/- 1.6 micromol approximately P muscle(-1)). The ratio of high-energy phosphate consumption to force-time-integral was significantly lower for lengthening [0.3 +/- 0.1 micromol approximately P (N s)(-1)] and isometric [0.6 +/- 0.2 micromol approximately P (N s)(-1)] contractions compared with shortening [1.2 +/- 0.2 micromol approximately P (N s)(-1)] contractions (P < 0.05).
CONCLUSION
The present results of maximally stimulated muscles are comparable with data in the literature for voluntary human exercise showing that the energy cost of force production during lengthening exercise is approximately 30% of that in shortening exercise. The present study suggests that this finding in humans probably does reflect intrinsic muscle properties rather than effects of differential recruitment and/or coactivation.
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