Skeletal muscle fatigue in old age: whose advantage?

Abstract

The results of recent studies indicate that in healthy men and women aged beyond approximately 65 years, the energy-producing pathways in skeletal muscle may combine with changes in motor unit behavior and muscle contractile properties to provide a unique environment for resisting muscle fatigue under some conditions.

Figure 1

Potential sites of failure during muscular activity. A model of the pathway of force production, useful for studies of the mechanisms of fatigue in vivo. Impairment at any site could result in a decrease in force or power output, indicating muscle fatigue. See text for details.

Figure 2

Target force, fatigue and intracellular pH in young (solid symbols) and older (open symbols) groups during incremental contractions. MVC; maximal voluntary contraction, obtained every 2 min. While both groups attained target level through 12 min of contractions (top panel), the older group had less fatigue (fall of MVC, middle panel) and acidosis (bottom panel) compared to young. Modified from J Appl Physiol 93:1813–1823, 2002. Used with permission.

Figure 3

Relative contribution from the 3 pathways of adenosine triphosphate (ATP) production during a sustained maximal voluntary contraction (MVC) in young (top) and older (bottom) groups. Percentages of total ATP from the creatine kinase reaction (hatched bar), oxidative phosphorylation (gray bar) and glycolysis (black bar) are shown. Older group generated relatively more ATP from oxidative phosphorylation than young group. J Appl Physiol 99:1736–1744, 2005. Used with permission.

Figure 4

Fatigue (left) and intracellular pH (right) during intermittent dorsiflexion maximal voluntary contractions (MVC) under free-flow (top) and ischemic (bottom) conditions. Open symbols indicate older group; solid symbols indicate young group. Hatched bars indicate contraction. FTI; force-time integral. Data are mean ± SE. Modified from J Physiol 583.3:1093–1105, 2007. Used with permission.

Figure 5

Metabolic economy in young (solid bars) and older (open bars) groups during intermittent maximal voluntary contractions (MVC). Older group had a higher metabolic economy (ME) than young group. Data are mean ± SE. See text for details.

Figure 6

Hypothetical sources and impact of increased metabolic economy in older skeletal muscle. Proposed scenario that may provide older muscle an advantage in terms of fatigue resistance, with the mechanisms of this advantage residing in both the neural and muscular systems. See text for details.