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C57BL/6 life span study: age-related declines in muscle power production and contractile velocity.

Graber TG, Kim JH, Grange RW, McLoon LK, Thompson LV - Age (Dordr) (2015)

Bottom Line: We hypothesized and found that power decreased with age not only at P max but also over the load range.Importantly, we found greater age-associated deficits in both power and velocity when the muscles were contracting concentrically against heavy loads (>50 % P 0).The results demonstrate that age-associated difficulty in movement during challenging tasks is likely due, in addition to overall reduced force output, to an accelerated deterioration of power production and contractile velocity under heavily loaded conditions.

View Article: PubMed Central - PubMed

Affiliation: Program in Physical Therapy, Department of Physical Medicine and Rehabilitation, University of Minnesota Medical School, Rm 366A Children's Rehab Center, 426 Church Street SE, Minneapolis, MN, 55455, USA, grab0170@umn.edu.

ABSTRACT
Quantification of key outcome measures in animal models of aging is an important step preceding intervention testing. One such measurement, skeletal muscle power generation (force * velocity), is critical for dynamic movement. Prior research focused on maximum power (P max), which occurs around 30-40 % of maximum load. However, movement occurs over the entire load range. Thus, the primary purpose of this study was to determine the effect of age on power generation during concentric contractions in the extensor digitorum longus (EDL) and soleus muscles over the load range from 10 to 90 % of peak isometric tetanic force (P 0). Adult, old, and elderly male C57BL/6 mice were examined for contractile function (6-7 months old, 100 % survival; ~24 months, 75 %; and ~28 months, <50 %, respectively). Mice at other ages (5-32 months) were also tested for regression modeling. We hypothesized and found that power decreased with age not only at P max but also over the load range. Importantly, we found greater age-associated deficits in both power and velocity when the muscles were contracting concentrically against heavy loads (>50 % P 0). The shape of the force-velocity curve also changed with age (a/P 0 increased). In addition, there were prolonged contraction times to maximum force and shifts in the distribution of the myosin light and heavy chain isoforms in the EDL. The results demonstrate that age-associated difficulty in movement during challenging tasks is likely due, in addition to overall reduced force output, to an accelerated deterioration of power production and contractile velocity under heavily loaded conditions.

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EDL velocity and power at heavier loads show increased age-related rate of decline. a Velocity. b Power equation: simple linear regression of % reduction in velocity and power of elderly mice (in comparison to adult mice) as a function of load (% P0). Light loads (10–40 % P0) are represented by diamonds with a dashed regression line and heavy loads (40–90 % P0) are represented by circles and a solid regression line; 40 % P0 is the inflection point indicating where the slope changes, and as such, the point is included in both sections of the graph. * = slope of line significantly different, p = 0.003 and p < 0.001 for velocity and power, respectively
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Fig2: EDL velocity and power at heavier loads show increased age-related rate of decline. a Velocity. b Power equation: simple linear regression of % reduction in velocity and power of elderly mice (in comparison to adult mice) as a function of load (% P0). Light loads (10–40 % P0) are represented by diamonds with a dashed regression line and heavy loads (40–90 % P0) are represented by circles and a solid regression line; 40 % P0 is the inflection point indicating where the slope changes, and as such, the point is included in both sections of the graph. * = slope of line significantly different, p = 0.003 and p < 0.001 for velocity and power, respectively

Mentions: While Vmax (unloaded velocity) did not change, age exerted a greater effect on EDL contractile velocity as the muscles contracted under increased loads (simple regression of the percent reduction and % P0: %Velocity = 0.33 (% P0) + 5.7, R = 0.985) (data not shown). The mean velocity percentage (average percent change at all measured loads) was reduced twofold at heavier loads (40–90 % P0) to 28 %, in comparison to lighter loads (reduced 14 % from 10 to 40 % P0) (Table 1 and Fig. 2a). There was an additional age-related decline of 65 % (slope of simple linear regression lines) at the heavier loads in comparison to the lighter loads [from separate linear regressions: %Velocity @ 10–40 % P0 = 0.23 (% P0) + 8.0, R = 0.994; %Velocity @ 40–80 % P0 = 0.38 (% P0) + 2.1, R = 0.972]. The slopes of these regression lines were different (p = 0.003, from the general linear model) (Fig. 2).Fig. 2


C57BL/6 life span study: age-related declines in muscle power production and contractile velocity.

Graber TG, Kim JH, Grange RW, McLoon LK, Thompson LV - Age (Dordr) (2015)

EDL velocity and power at heavier loads show increased age-related rate of decline. a Velocity. b Power equation: simple linear regression of % reduction in velocity and power of elderly mice (in comparison to adult mice) as a function of load (% P0). Light loads (10–40 % P0) are represented by diamonds with a dashed regression line and heavy loads (40–90 % P0) are represented by circles and a solid regression line; 40 % P0 is the inflection point indicating where the slope changes, and as such, the point is included in both sections of the graph. * = slope of line significantly different, p = 0.003 and p < 0.001 for velocity and power, respectively
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4401475&req=5

Fig2: EDL velocity and power at heavier loads show increased age-related rate of decline. a Velocity. b Power equation: simple linear regression of % reduction in velocity and power of elderly mice (in comparison to adult mice) as a function of load (% P0). Light loads (10–40 % P0) are represented by diamonds with a dashed regression line and heavy loads (40–90 % P0) are represented by circles and a solid regression line; 40 % P0 is the inflection point indicating where the slope changes, and as such, the point is included in both sections of the graph. * = slope of line significantly different, p = 0.003 and p < 0.001 for velocity and power, respectively
Mentions: While Vmax (unloaded velocity) did not change, age exerted a greater effect on EDL contractile velocity as the muscles contracted under increased loads (simple regression of the percent reduction and % P0: %Velocity = 0.33 (% P0) + 5.7, R = 0.985) (data not shown). The mean velocity percentage (average percent change at all measured loads) was reduced twofold at heavier loads (40–90 % P0) to 28 %, in comparison to lighter loads (reduced 14 % from 10 to 40 % P0) (Table 1 and Fig. 2a). There was an additional age-related decline of 65 % (slope of simple linear regression lines) at the heavier loads in comparison to the lighter loads [from separate linear regressions: %Velocity @ 10–40 % P0 = 0.23 (% P0) + 8.0, R = 0.994; %Velocity @ 40–80 % P0 = 0.38 (% P0) + 2.1, R = 0.972]. The slopes of these regression lines were different (p = 0.003, from the general linear model) (Fig. 2).Fig. 2

Bottom Line: We hypothesized and found that power decreased with age not only at P max but also over the load range.Importantly, we found greater age-associated deficits in both power and velocity when the muscles were contracting concentrically against heavy loads (>50 % P 0).The results demonstrate that age-associated difficulty in movement during challenging tasks is likely due, in addition to overall reduced force output, to an accelerated deterioration of power production and contractile velocity under heavily loaded conditions.

View Article: PubMed Central - PubMed

Affiliation: Program in Physical Therapy, Department of Physical Medicine and Rehabilitation, University of Minnesota Medical School, Rm 366A Children's Rehab Center, 426 Church Street SE, Minneapolis, MN, 55455, USA, grab0170@umn.edu.

ABSTRACT
Quantification of key outcome measures in animal models of aging is an important step preceding intervention testing. One such measurement, skeletal muscle power generation (force * velocity), is critical for dynamic movement. Prior research focused on maximum power (P max), which occurs around 30-40 % of maximum load. However, movement occurs over the entire load range. Thus, the primary purpose of this study was to determine the effect of age on power generation during concentric contractions in the extensor digitorum longus (EDL) and soleus muscles over the load range from 10 to 90 % of peak isometric tetanic force (P 0). Adult, old, and elderly male C57BL/6 mice were examined for contractile function (6-7 months old, 100 % survival; ~24 months, 75 %; and ~28 months, <50 %, respectively). Mice at other ages (5-32 months) were also tested for regression modeling. We hypothesized and found that power decreased with age not only at P max but also over the load range. Importantly, we found greater age-associated deficits in both power and velocity when the muscles were contracting concentrically against heavy loads (>50 % P 0). The shape of the force-velocity curve also changed with age (a/P 0 increased). In addition, there were prolonged contraction times to maximum force and shifts in the distribution of the myosin light and heavy chain isoforms in the EDL. The results demonstrate that age-associated difficulty in movement during challenging tasks is likely due, in addition to overall reduced force output, to an accelerated deterioration of power production and contractile velocity under heavily loaded conditions.

Show MeSH
Related in: MedlinePlus