Walking energetics, fatigability, and fatigue in older adults: the study of energy and aging pilot

BACKGROUND

Slow gait speed increases morbidity and mortality in older adults. We examined how preferred gait speed is associated with energetic requirements of walking, fatigability, and fatigue.

METHODS

Older adults (n = 36, 70-89 years) were categorized as slow or fast walkers based on median 400-m gait speed. We measured VO2peak by graded treadmill exercise test and VO2 during 5-minute treadmill walking tests at standard (0.72 m/s) and preferred gait speeds. Fatigability was assessed with the Situational Fatigue Scale and the Borg rating of perceived exertion at the end of walking tests. Fatigue was assessed by questionnaire.

RESULTS

Preferred gait speed over 400 m (range: 0.75-1.58 m/s) averaged 1.34 m/s for fast walkers versus 1.05 m/s for slow walkers (p < .001). VO2peak was 26% lower (18.5 vs 25.1ml/kg/min, p = .001) in slow walkers than fast walkers. To walk at 0.72 m/s, slow walkers used a larger percentage of VO2peak (59% vs 42%, p < .001). To walk at preferred gait speed, slow walkers used more energy per unit distance (0.211 vs 0.186ml/kg/m, p = .047). Slow walkers reported higher rating of perceived exertion during walking and greater overall fatigability on the Situational Fatigue Scale, but no differences in fatigue.

CONCLUSIONS

Slow walking was associated with reduced aerobic capacity, greater energetic cost of walking, and greater fatigability. Interventions to improve aerobic capacity or decrease energetic cost of walking may prevent slowing of gait speed and promote mobility in older adults.

Skeletal Muscle Mitochondrial Function and Fatigability in Older Adults

BACKGROUND

Fatigability increases while the capacity for mitochondrial energy production tends to decrease significantly with age. Thus, diminished mitochondrial function may contribute to higher levels of fatigability in older adults.

METHODS

The relationship between fatigability and skeletal muscle mitochondrial function was examined in 30 participants aged 78.5 ± 5.0 years (47% female, 93% white), with a body mass index of 25.9 ± 2.7 kg/m(2) and usual gait-speed of 1.2 ± 0.2 m/s. Fatigability was defined using rating of perceived exertion (6-20 point Borg scale) after a 5-minute treadmill walk at 0.72 m/s. Phosphocreatine recovery in the quadriceps was measured using (31)P magnetic resonance spectroscopy and images of the quadriceps were captured to calculate quadriceps volume. ATPmax (mM ATP/s) and oxidative capacity of the quadriceps (ATPmax·Quadriceps volume) were calculated. Peak aerobic capacity (VO2peak) was measured using a modified Balke protocol.

RESULTS

ATPmax·Quadriceps volume was associated with VO2peak and was 162.61mM ATP·mL/s lower (p = .03) in those with high (rating of perceived exertion ≥10) versus low (rating of perceived exertion ≤9) fatigability. Participants with high fatigability required a significantly higher proportion of VO2peak to walk at 0.72 m/s compared with those with low fatigability (58.7 ± 19.4% vs 44.9 ± 13.2%, p < .05). After adjustment for age and sex, higher ATPmax was associated with lower odds of having high fatigability (odds ratio: 0.34, 95% CI: 0.11-1.01, p = .05).

CONCLUSIONS

Lower capacity for oxidative phosphorylation in the quadriceps, perhaps by contributing to lower VO2peak, is associated with higher fatigability in older adults.

Bed rest promotes reductions in walking speed, functional parameters, and aerobic fitness in older, healthy adults

CONTEXT

The exact relationship between the bed rest-induced loss of skeletal muscle and reductions in muscle strength and physical performance in the older individuals is still unclear.

OBJECTIVE

We examined the effect of 10 days of bed rest on changes in regional body composition, muscle strength, and functional status, and the relationship between these variables in older individuals.

DESIGN, PARTICIPANTS, AND INTERVENTION

Regional body composition was measured using dual energy x-ray absorptiometry. We also determined changes in leg strength and several indices of functional status, including walking speed.

RESULTS

Body weight, body mass index, and total and lower extremity lean mass decreased with bed rest. There were also significant reductions in knee extension one repetition maximum, isometric knee extension, knee extension 60° concentric, stair ascent time, stair ascent power, stair descent time, VO2 max, floor transfer test, 5-minute walk time, and chair stand. The overall change in total and lower extremity lean mass was also directly related to bed rest-induced reductions in one repetition maximum knee extension.

CONCLUSIONS

Bed rest promoted overall declines in muscle mass, muscle strength, and physical function in older individuals. The changes in lean tissue were closely correlated with the bed rest-induced decline of muscle strength.

Effects of lower limb length and body proportions on the energy cost of overground walking in older persons

Background. Although walking has been extensively investigated in its biomechanical and physiological aspects, little is known on whether lower limb length and body proportions affect the energy cost of overground walking in older persons. Methods. We enrolled 50 men and 12 women aged 65 years and over, mean 69.1 ± SD 5.4, who at the end of their cardiac rehabilitation program performed the six-minute walk test while wearing a portable device for direct calorimetry and who walked a distance comparable to that of nondisabled community-dwelling older persons. Results. In the multivariable regression model (F = 12.75, P < 0.001, adjusted R² = 0.278) the energy cost of overground walking, expressed as the net energy expenditure, in kg⁻¹ sec⁻¹, needed to provide own body mass with 1 joule kinetic energy, was inversely related to lower limb length and directly related to lower limb length to height ratio (β ± SE(β) = −3.72∗10⁻³ ± 0.74∗10⁻³, P < 0.001, and 6.61∗10⁻³ ± 2.14∗10⁻³, P = 0.003, resp.). Ancillary analyses also showed that, altogether, 1 cm increase in lower limb length reduced the energy cost of overground walking by 2.57% (95%CI 2.35–2.79). Conclusions. Lower limb length and body proportions actually affect the energy cost of overground walking in older persons.

Feasibility of a combined aerobic and strength training program and its effects on cognitive and physical function in institutionalized dementia patients. A pilot study

Objectives

We examined the feasibility of a combined aerobic and strength training program in institutionalized dementia patients and studied the effects on cognitive and physical function.

Methods

Thirty-three patients with dementia, recruited from one nursing home, participated in this non-randomized pilot study (25 women; age = 85.2±4.9 years; Mini Mental State Examination = 16.8±4.0). In phase 1 of the study, seventeen patients in the Exercise group (EG) received a combined aerobic and strength training program for six weeks, five times per week, 30 minutes per session, in an individually supervised format and successfully concluded the pre and posttests. In phase 2 of the study, sixteen patients in the Social group (SG) received social visits at the same frequency, duration, and format and successfully concluded the pre and posttests.

Results

Indices of feasibility showed that the recruitment and adherence rate, respectively were 46.2% and 86.3%. All EG patients completed the exercise program according to protocol without adverse events. After the six-week program, no significant differences on cognitive function tests were found between the EG and SG. There was a moderate effect size in favor for the EG for the Visual Memory Span Forward; a visual attention test. There were significant differences between groups in favor for the EG with moderate to large effects for the physical tests Walking Speed (p = .003), Six-Minute Walk Test (p = .031), and isometric quadriceps strength (p = .012).

Conclusions

The present pilot study showed that it is feasible to conduct a combined aerobic and strength training program in institutionalized patients with dementia. The selective cognitive visual attention improvements and more robust changes in motor function in favor of EG vs. SG could serve as a basis for large randomized clinical trials.

Trial Registration

trialregister.nl 1230

Walking speed: the functional vital sign

Walking speed (WS) is a valid, reliable, and sensitive measure appropriate for assessing and monitoring functional status and overall health in a wide range of populations. These capabilities have led to its designation as the "sixth vital sign". By synthesizing the available evidence on WS, this scholarly review article provides clinicians with a reference tool regarding this robust measure. Recommendations on testing procedures for assessing WS, including optimal distance, inclusion of acceleration and deceleration phases, instructions, and instrumentation are given. After assessing an individual's WS, clinicians need to know what this value represents. Therefore, WS cut-off values and the corresponding predicted outcomes, as well as minimal detectable change values for specific populations and settings are provided.

The association between energy cost of walking and physical function in older adults

To assess the association between energy cost of walking and self-report of function, independent of comorbidity and gait speed, in older adults with mobility limitations. This cross-sectional observational study was conducted within an ambulatory clinical research training center. Forty-two older adults, age 65 and older, with slow and variable gait participated. Function was assessed using the Late Life Function and Disability Index-Basic Lower Extremity Subscale, while energy cost of walking was derived by standardizing the mean oxygen consumption recorded during physiological steady state by gait speed. Comorbidity and gait speed were collected as co-variates. Pearson's r correlation coefficient and regression analyses were used to assess the relationship between energy cost and function. Energy cost of walking was significantly correlated with self-reported function (Pearson's r=-0.50, p<0.001); furthermore, energy cost of walking explained an additional 17% (p=0.002) of the variance in self-reported function above and beyond the variance explained by comorbidity and gait speed combined. Energy cost of walking is emerging as another significant factor related to functional performance among older adults, even after controlling for comorbidity and gait speed - robust variables known for their strong contributions to function. Knowledge of and attention to the efficiency of how one moves (high energy cost of walking) may enhance rehabilitation efforts to further reduce "functional burden" in older adults.

Gait speed correlates in a multiracial population of community-dwelling older adults living in Brazil: a cross-sectional population-based study

Background

Gait speed is a strong predictor of a wide range of adverse health outcomes in older adults. Mean values for gait speed in community-dwelling older adults vary substantially depending on population characteristics, suggesting that social, biological, or health factors might explain why certain groups tend to self-select their gait speed in different patterns. The vast majority of studies reported in the literature present data from North American and European populations. There are few population-based studies from other regions with a different ethnicity and/or social and health conditions. To address this, the present study identified the mean usual and fast gait speeds in a representative multiracial population of community-dwelling older adults living in a developing country, and explored their association with sociodemographic, mental and physical health characteristics.

Methods

This was a cross-sectional population-based study of a sample of 137 men and 248 women, aged 65 years and over. Usual gait speed and fast gait speed were measured on a 4.6 m path. Participants were classified into slow, intermediate, and faster groups by cluster analysis. Logistic regression analysis was used to estimate the independent effect of each factor on the odds of presenting with a slower usual and slower fast gait speeds.

Results

Participants had a mean (SD) usual gait speed of 1.11 (0.27) m/s and a mean fast gait speed of 1.39 (0.34) m/s. We did not observe an independent association between gait speed and race/ethnicity, educational level, or income. The main contributors to present a slower usual gait speed were low physical activity level, stroke, diabetes, urinary incontinence, high concern about falling, and old age. A slower fast gait speed was associated with old age, low physical activity, urinary incontinence and high concern about falling.

Conclusion

A multiracial population of older adults living in a developing country showed a similar mean gait speed to that observed in previously studied populations. The results suggest that low physical activity, urinary incontinence and high concern about falling should not be neglected and may help identify those who might benefit from early intervention.

The relationship of the energetic cost of slow walking and peak energy expenditure to gait speed in mid-to-late life

OBJECTIVE

Peak energy expenditure is highly correlated with usual gait speed; however, it is unknown whether the energetic cost of walking is also an important contributor to usual gait speed when considered as a component of peak walking capacity.

DESIGN

The energetic cost of 5 mins of slow treadmill walking (0.67 m/sec), peak overground walking energy expenditure, and usual gait speed over 6 m were assessed cross-sectionally in 405 adults aged 33 to 94 yrs in the Baltimore Longitudinal Study of Aging.

RESULTS

Mean (SD) energy expenditures during slow and peak sustained walking were 8.9 (1.4) and 18.38 (4.8) ml kg(-1) min(-1), respectively. Overall, the energetic cost of slow walking as a percentage of peak walking energy expenditure was strongly associated with usual gait speed (P < 0.001); however in stratified analyses, this association was maintained only in those with peak walking capacity below 18.3 ml kg(-1) min(-1) (P = 0.04), the threshold associated with independent living.

CONCLUSIONS

In older persons with substantially reduced peak walking capacity, the energetic cost of walking is associated with gait speed, particularly when peak walking capacity nears the minimum level considered necessary for independent living. Thus, optimal habilitation in older frail persons may benefit from both improving fitness and reducing the energetic cost of walking.

Resilience, physical performance measures, and self-perceived physical and mental health in older Catholic nuns

BACKGROUND AND PURPOSE

The importance of physical performance measures and their influence on predicting future disability has been suggested; however, the association between resilience and physical performance measures in older women needs further study. The purpose of this research study was to investigate the resilience level in a convenience sample of older women who happened to be Roman Catholic nuns. The relationships of resilience with specific physical performance measures, self-perceived physical and mental health status, and depressive symptoms were also explored.

METHODS

Descriptive correlational cross-sectional design was used. Data from 54 volunteer Roman Catholic nuns, aged 55-94 were collected beginning with self report questionnaires followed by physical performance tests. Self-report measures included the Resilience Scale, Short-Form revised (SF-12v2) Health Survey, and Patient Health Questionnaire (PHQ-9). The 12-point Short Physical Performance Battery (SPPB) and fast gait speed were the physical performance tests measured.

RESULTS

This sample of nuns had moderate levels of resilience. Those with fewer depressive symptoms and better health had higher resilience levels. Fast gait speed was positively associated with resilience.

DISCUSSION

The positive relationship between resilience and gait speed is an important finding of this study because it reinforces the connection between physical and emotional health. Future studies should examine if resilience and gait speed can serve as predictors of disability in a broader sample of older adults or if resilience can be targeted as a means of improving physical performance.

CONCLUSION

Maintaining functional ability and recovering when physical injury is experienced is of great importance in older adults. It is reasonable for physical therapists to consider both resilience and physical performance measures when attempting to identify older women at risk for poor outcomes. Resilience may play a role in helping older adults recover from a physical injury.

The role of energetic cost in the age-related slowing of gait speed

OBJECTIVES

To determine whether slow gait represents a compensatory strategy to reduce the energetic cost of walking with age.

DESIGN

Cross-sectional analysis.

SETTING

Community-dwelling volunteers from the Baltimore Longitudinal Study of Aging (BLSA).

PARTICIPANTS

Four hundred twenty community-dwelling persons aged 32 to 96 (mean 68.1 ± 12.5) who underwent a physical examination, physical function testing, and energy expenditure assessment.

MEASUREMENTS

Energy expenditure per minute (mL/kg/min) and per meter (mL/kg/m) during 2.5 minutes of overground walking at customary speed and usual gait speed over 6 m (m/s) were examined. General linear regression models were used to assess the relationship between customary walking energy expenditure and usual gait speed, adjusted for potential confounders including smoking, medical diagnoses, walking-related pain, and balance difficulty.

RESULTS

Usual gait speed was slower with increasing age after age 65. Energy expenditure per minute during customary walking averaged 13.0 ± 2.8 mL/kg/min and was independent of age (ρ < 0.01, P = .88). In contrast, energy expenditure per meter walked was progressively higher after age 65 (ρ = 0.35, P < .001) and heightened after age 80 (r = 0.57, P < .001), mirroring the observed pattern of usual gait speed. This relationship remained significant after adjusting for multiple impairments and comorbidities.

CONCLUSION

These observations support the hypothesis that slower gait at older ages may reflect a compensatory action to offset the greater energetic cost of walking associated with aging and chronic conditions. Future studies should evaluate the specific mechanisms that contribute to this phenomenon as novel targets for clinical intervention.

Perceived effort of walking: relationship with gait, physical function and activity, fear of falling, and confidence in walking in older adults with mobility limitations

BACKGROUND

Although clinicians have a number of measures to use to describe walking performance, few, if any, of the measures capture a person's perceived effort in walking. Perceived effort of walking may be a factor in what a person does versus what he or she is able to do.

OBJECTIVE

The objective of this study was to examine the relationship of perceived effort of walking with gait, function, activity, fear of falling, and confidence in walking in older adults with mobility limitations. Design This investigation was a cross-sectional, descriptive, relational study.

METHODS

The study took place at a clinical research training center. The participants were 50 older adults (mean age=76.8 years, SD=5.5) with mobility limitations. The measurements used were the Rating of Perceived Exertion (RPE) for walking; gait speed; the Modified Gait Abnormality Rating Scale; energy cost of walking; Late Life Function and Disability Instrument (LLFDI) for total, basic, and advanced lower-extremity function and for disability limitations; activity and restriction subscales of the Survey of Activities and Fear of Falling in the Elderly (SAFFE); activity counts; SAFFE fear subscale; and Gait Efficacy Scale (GES). The relationship of the RPE of walking with gait, function, activity, fear, and confidence was determined by using Spearman rank order coefficients and an analysis of variance (adjusted for age and sex) for mean differences between groups defined by no exertion during walking and some exertion during walking.

RESULTS

The RPE was related to confidence in walking (GES, R=-.326, P=.021) and activity (activity counts, R=.295, P=.044). The RPE groups (no exertion versus some exertion) differed in LLFDI scores for total (57.9 versus 53.2), basic (68.6 versus 61.4), and advanced (49.1 versus 42.6) lower-extremity function; LLFDI scores for disability limitations (74.9 versus 67.5); SAFFE fear subscale scores (0.346 versus 0.643); and GES scores (80.1 versus 67.8) (all P<.05). Limitations The range of RPE scores for the participants studied was narrow. Thus, the real correlations between RPE and gait, physical function, and psychological aspects of walking may be greater than the relationships reported.

CONCLUSIONS

The perceived effort of walking was associated with physical activity and confidence in walking. Reducing the perceived effort of walking may be an important target of interventions to slow the decline in function of older adults with mobility limitations.

Gait speed as a measure in geriatric assessment in clinical settings: a systematic review

BACKGROUND

Gait speed is a quick, inexpensive, reliable measure of functional capacity with well-documented predictive value for major health-related outcomes. Numerous epidemiological studies have documented gait speed in healthy, community-dwelling older people. The purpose of this study is to undertake a systematic review and meta-analysis of gait speed in a specific group with mobility limitations-geriatric patients in clinical settings.

METHODS

Relevant databases were searched systematically for original research articles published in February 2011 measuring gait speed in persons aged 70 or older in hospital inpatient or outpatients settings. Meta-analysis determined gait speed data for each setting adjusting for covariates.

RESULTS

The review included 48 studies providing data from 7,000 participants. Across the hospital settings, the gait speed estimate for usual pace was 0.58 m/s (95% confidence interval [CI]: 0.49-0.67) and for maximal pace was 0.89 m/s (95% CI: 0.75-1.02). These estimates were based on most recent year of publication (2011) and median percentage of female participants (63%). Gait speed at usual pace in acute care settings was 0.46 m/s (95% CI: 0.34-0.57), which was significantly slower than the gait speed of 0.74 m/s (95% CI: 0.65-0.83) recorded in outpatient settings.

CONCLUSIONS

Gait speed is an important measure in comprehensive geriatric assessment. The consolidation of data from multiple studies reported in this meta-analysis highlights the mobility limitations experienced by older people in clinical settings and the need for ongoing rehabilitation to attain levels sufficient for reintegration in the community.

Does the attentional demands of walking differ for older men and women living independently in the community?

BACKGROUND AND PURPOSE

Walking has been shown to be an attentionally demanding task. For older adults, gender-specific differences in gait and falling reported in the literature could arise as a result of the attentional demands of walking. However, differences in how older men and women allocate attention to walking have not been investigated. The purpose of this study was to use a dual-task voice reaction time paradigm to examine gender-specific differences in the attentional demands of walking in older adults who are independent in community ambulation.

METHODS

A dual-task paradigm was used to measure voice reaction time (VRT) in older community-dwelling men (n = 29; mean age = 78.40, SD = 6.17 years) and women (n = 33; mean age = 77.01, SD = 6.07 years) under 3 task conditions: sitting in a chair, standing, and walking on a level surface. Between- and within-group differences in dual-task VRT were examined using a 2 (men vs women) by 3 (task condition) repeated-measures analysis of variance. The level of statistical significance was set at 0.05, and a Bonferroni procedure was used for post hoc analyses.

RESULTS

Sitting VRT was similar for men (mean = 454.90, SD = 140.05 milliseconds) and women (mean = 454.49, SD = 94.27 milliseconds). While standing, men had a slightly faster VRT (mean = 444.90, SD = 125.31 milliseconds vs mean = 452.09, SD = 92.82 milliseconds). When walking, VRT increased for both groups in comparison to sitting and standing and older men (mean = 509.11, SD = 142.19 milliseconds) responded faster than older women (mean = 537.55, SD = 122.43). However, the main effect of gender (P = .665) and interaction of gender with task (P = .433) were both not statistically significant. A statistically significant main effect for task (P < .001) indicated that walking VRT (mean = 524.25, SD = 131.71 milliseconds) was significantly longer than both sitting (P < .001, mean = 454.68, SD = 116.89 milliseconds) and standing (P < .001, mean = 448.36, SD = 108.37 milliseconds) VRT.

DISCUSSION

The results demonstrate that the attentional demands of walking are not different for older adult men and women who are independent in community mobility. However, support was provided for the idea that walking is an attentionally demanding activity. In comparison with sitting and standing, walking was more attentionally demanding for both men and women. CONCLUSIONS.: A dual-task voice reaction time paradigm revealed that walking is not more attentionally demanding on the basis of gender when comparing community-dwelling older adult men with women.

The improvement of walking speed after cardiac rehabilitation is associated with the reduction in the metabolic cost of walking in older persons

BACKGROUND

To walk a given distance older persons consume more metabolic energy than younger adults across all speeds. As physical activity interventions improve a variety of physical performance measures in older persons, including walking speed, in this study we hypothesized that the improvement of walking speed might be associated with the reduction of the metabolic cost of walking and we tested our hypothesis in a selected sample of older patients receiving cardiac rehabilitation.

METHODS

In 120 patients (88 men and 32 women, mean age 74.1 years±SD 5.0) we assessed energy expenditure during the 6-min Walk Test (6mWT) before and after the rehabilitation using a portable system for direct calorimetry.

RESULTS

On the 6mWT performed after the rehabilitation patients significantly increased total energy expenditure (28.0 kcal±SD 8.3 vs. 25.7 kcal±SD 7.6, p<0.001), the distance walked (398 m±SD 93 vs. 343 m±SD 95, p<0.001) and, consequently, walking speed (1.11 m/s±SD 0.26 vs. 0.95m/s±SD 0.26, p<0.001) while the metabolic cost of walking, i.e. the amount of energy used to move a body mass of 1 kg for a distance of 1m, was significantly reduced (1.00 cal/kg/m±SD 0.19 vs. 1.11 cal/kg/m±SD 0.32, p<0.001).

CONCLUSIONS

In older patients receiving cardiac rehabilitation the improvement of walking speed is associated with the improvement of walking economy. This might be a contributory factor to the favourable effects of physical activity interventions on physical performance measures.

Impaired economy of gait and decreased six-minute walk distance in Parkinson's disease

Changes in the biomechanics of gait may alter the energy requirements of walking in Parkinson's Disease (PD). This study investigated economy of gait during submaximal treadmill walking in 79 subjects with mild to moderate PD and the relationship between gait economy and 6-minute walk distance (6 MW). Oxygen consumption (VO(2)) at the self-selected treadmill walking speed averaged 64% of peak oxygen consumption (VO(2) peak). Submaximal VO(2) levels exceeded 70% of VO(2) peak in 30% of the subjects. Overall the mean submaximal VO(2) was 51% higher than VO(2) levels expected for the speed and grade consistent with severe impairment in economy of gait. There was an inverse relationship between economy of gait and 6MW (r = -0.31, P < 0.01) and with the self-selected walking speed (r = -0.35, P < 0.01). Thus, the impairment in economy of gait and decreased physiologic reserve result in routine walking being performed at a high percentage of VO(2) peak.

Reduced satellite cell numbers and myogenic capacity in aging can be alleviated by endurance exercise

Background

Muscle regeneration depends on satellite cells, myogenic stem cells that reside on the myofiber surface. Reduced numbers and/or decreased myogenic aptitude of these cells may impede proper maintenance and contribute to the age-associated decline in muscle mass and repair capacity. Endurance exercise was shown to improve muscle performance; however, the direct impact on satellite cells in aging was not yet thoroughly determined. Here, we focused on characterizing the effect of moderate-intensity endurance exercise on satellite cell, as possible means to attenuate adverse effects of aging. Young and old rats of both genders underwent 13 weeks of treadmill-running or remained sedentary.

Methodology

Gastrocnemius muscles were assessed for the effect of age, gender and exercise on satellite-cell numbers and myogenic capacity. Satellite cells were identified in freshly isolated myofibers based on Pax7 immunostaining (i.e., ex-vivo). The capacity of individual myofiber-associated cells to produce myogenic progeny was determined in clonal assays (in-vitro). We show an age-associated decrease in satellite-cell numbers and in the percent of myogenic clones in old sedentary rats. Upon exercise, there was an increase in myofibers that contain higher numbers of satellite cells in both young and old rats, and an increase in the percent of myogenic clones derived from old rats. Changes at the satellite cell level in old rats were accompanied with positive effects on the lean-to-fat Gast muscle composition and on spontaneous locomotion levels. The significance of these data is that they suggest that the endurance exercise-mediated boost in both satellite numbers and myogenic properties may improve myofiber maintenance in aging.