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Age- and gender-related changes in contractile properties of non-atrophied EDL muscle.

Chan S, Head SI - PLoS ONE (2010)

Bottom Line: However, it is not entirely clear whether these changes in contractile properties can occur before there is significant atrophy, and whether males and females are affected differently.In the properties of absolute force and muscle relaxation times, females were affected by ageing to a greater extent than males.Our findings provide further insight into the muscle atrophy, weakness and fatiguability experienced by the elderly.

View Article: PubMed Central - PubMed

Affiliation: School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia.

ABSTRACT

Background: In humans, ageing causes skeletal muscles to become atrophied, weak, and easily fatigued. In rodent studies, ageing has been associated with significant muscle atrophy and changes in the contractile properties of the muscles. However, it is not entirely clear whether these changes in contractile properties can occur before there is significant atrophy, and whether males and females are affected differently.

Methods and results: We investigated various contractile properties of whole isolated fast-twitch EDL muscles from adult (2-6 months-old) and aged (12-22 months-old) male and female mice. Atrophy was not present in the aged mice. Compared with adult mice, EDL muscles of aged mice had significantly lower specific force, longer tetanus relaxation times, and lower fatiguability. In the properties of absolute force and muscle relaxation times, females were affected by ageing to a greater extent than males. Additionally, EDL muscles from a separate group of male mice were subjected to eccentric contractions of 15% strain, and larger force deficits were found in aged than in adult mice.

Conclusion: Our findings provide further insight into the muscle atrophy, weakness and fatiguability experienced by the elderly. We have shown that even in the absence of muscle atrophy, there are definite alterations in the physiological properties of whole fast-twitch muscle from ageing mice, and for some of these properties the alterations are more pronounced in female mice than in male mice.

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Tetanus relaxation.(A) shows force recordings of the tetanus for two EDL muscles in our sample. It shows the final stages of the period of stimulation, and the initial stages of relaxation. It can be seen that force declines linearly in the initial stages of relaxation. In the muscle that relaxes more slowly (dashed line), this linear phase has a longer duration and a reduced steepness of slope compared with the faster-relaxing muscle (full line). We examined this linear phase both before and after subjecting the muscles to a fatiguing stimulation protocol. The duration of the linear phase is shown in (B) and the steepness of the slope of this linear phase is shown in (C).
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pone-0012345-g004: Tetanus relaxation.(A) shows force recordings of the tetanus for two EDL muscles in our sample. It shows the final stages of the period of stimulation, and the initial stages of relaxation. It can be seen that force declines linearly in the initial stages of relaxation. In the muscle that relaxes more slowly (dashed line), this linear phase has a longer duration and a reduced steepness of slope compared with the faster-relaxing muscle (full line). We examined this linear phase both before and after subjecting the muscles to a fatiguing stimulation protocol. The duration of the linear phase is shown in (B) and the steepness of the slope of this linear phase is shown in (C).

Mentions: Figure 4 shows our analysis of relaxation following tetanic stimulation in the EDL muscles of adult and aged male and female mice. Relaxation following tetanic stimulation generally occurs in two phases – an initial phase where force declines linearly, followed by a faster phase where force declines exponentially [28]. The intial linear phase is easier to interpret in terms of muscle relaxation [28] and hence this is the phase we have chosen to analyse. (A) is a recording of tetanus relaxation in two EDL muscles from our sample, showing muscle force in the final stages of stimulation and the initial stages of relaxation. Regression lines have been drawn to indicate the linear phase of relaxation. We measured the duration and slope (rate of force decline) of this linear phase, both before and after subjecting our sample of muscles to a fatiguing stimulation protocol (see Methods for fatigue protocol). The results for duration are shown in (B) and the results for rate of force decline are shown in (C).


Age- and gender-related changes in contractile properties of non-atrophied EDL muscle.

Chan S, Head SI - PLoS ONE (2010)

Tetanus relaxation.(A) shows force recordings of the tetanus for two EDL muscles in our sample. It shows the final stages of the period of stimulation, and the initial stages of relaxation. It can be seen that force declines linearly in the initial stages of relaxation. In the muscle that relaxes more slowly (dashed line), this linear phase has a longer duration and a reduced steepness of slope compared with the faster-relaxing muscle (full line). We examined this linear phase both before and after subjecting the muscles to a fatiguing stimulation protocol. The duration of the linear phase is shown in (B) and the steepness of the slope of this linear phase is shown in (C).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2925956&req=5

pone-0012345-g004: Tetanus relaxation.(A) shows force recordings of the tetanus for two EDL muscles in our sample. It shows the final stages of the period of stimulation, and the initial stages of relaxation. It can be seen that force declines linearly in the initial stages of relaxation. In the muscle that relaxes more slowly (dashed line), this linear phase has a longer duration and a reduced steepness of slope compared with the faster-relaxing muscle (full line). We examined this linear phase both before and after subjecting the muscles to a fatiguing stimulation protocol. The duration of the linear phase is shown in (B) and the steepness of the slope of this linear phase is shown in (C).
Mentions: Figure 4 shows our analysis of relaxation following tetanic stimulation in the EDL muscles of adult and aged male and female mice. Relaxation following tetanic stimulation generally occurs in two phases – an initial phase where force declines linearly, followed by a faster phase where force declines exponentially [28]. The intial linear phase is easier to interpret in terms of muscle relaxation [28] and hence this is the phase we have chosen to analyse. (A) is a recording of tetanus relaxation in two EDL muscles from our sample, showing muscle force in the final stages of stimulation and the initial stages of relaxation. Regression lines have been drawn to indicate the linear phase of relaxation. We measured the duration and slope (rate of force decline) of this linear phase, both before and after subjecting our sample of muscles to a fatiguing stimulation protocol (see Methods for fatigue protocol). The results for duration are shown in (B) and the results for rate of force decline are shown in (C).

Bottom Line: However, it is not entirely clear whether these changes in contractile properties can occur before there is significant atrophy, and whether males and females are affected differently.In the properties of absolute force and muscle relaxation times, females were affected by ageing to a greater extent than males.Our findings provide further insight into the muscle atrophy, weakness and fatiguability experienced by the elderly.

View Article: PubMed Central - PubMed

Affiliation: School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia.

ABSTRACT

Background: In humans, ageing causes skeletal muscles to become atrophied, weak, and easily fatigued. In rodent studies, ageing has been associated with significant muscle atrophy and changes in the contractile properties of the muscles. However, it is not entirely clear whether these changes in contractile properties can occur before there is significant atrophy, and whether males and females are affected differently.

Methods and results: We investigated various contractile properties of whole isolated fast-twitch EDL muscles from adult (2-6 months-old) and aged (12-22 months-old) male and female mice. Atrophy was not present in the aged mice. Compared with adult mice, EDL muscles of aged mice had significantly lower specific force, longer tetanus relaxation times, and lower fatiguability. In the properties of absolute force and muscle relaxation times, females were affected by ageing to a greater extent than males. Additionally, EDL muscles from a separate group of male mice were subjected to eccentric contractions of 15% strain, and larger force deficits were found in aged than in adult mice.

Conclusion: Our findings provide further insight into the muscle atrophy, weakness and fatiguability experienced by the elderly. We have shown that even in the absence of muscle atrophy, there are definite alterations in the physiological properties of whole fast-twitch muscle from ageing mice, and for some of these properties the alterations are more pronounced in female mice than in male mice.

Show MeSH
Related in: MedlinePlus