Steven A. Hawkins

Rate and mechanism of maximal oxygen consumption decline with aging: implications for exercise training.

Because of the influence of cardiorespiratory fitness on functional independence, quality of life, and cardiovascular disease and all-cause mortality, tremendous interest has been directed towards describing the age-related change in maximal oxygen consumption (V̇O2max). Current evidence supports a 10% per decade decline in V̇O2max in men and women regardless of activity level. High-intensity exercise may reduce this loss by up to 50% in young and middle-aged men, but not older men, if maintained long term. Middle-aged and older women do not appear to be able to reduce loss rates in V̇O2max to less than 10% per decade, which may be related to estrogen status. However, maintaining high-intensity training seems limited to approximately one decade at best and to a select few individuals. While the factors limiting the ability to maintain high-intensity training are not completely known, aging most likely plays a role as studies have demonstrated that training maintenance becomes more difficult with advancing age. Age-related loss of V̇O2max seems to occur in a non-linear fashion in association with declines in physical activity. In sedentary individuals, this non-linear decline generally occurs during the twenties and thirties whereas athletic individuals demonstrate a non-linear decline upon decreasing or ceasing training. Non-linear loss rates are also demonstrated in individuals over the age of 70 years. The decline in V̇O2max seems to be due to both central and peripheral adaptations, primarily reductions in maximal heart rate (HRmax) and lean body mass (LBM). Exercise training does not influence declines in HRmax, while LBM can be maintained to some degree by exercise. Recommendations for exercise training should include aerobic activities utilising guidelines established by the American College of Sports Medicine for improving CV fitness and health, as well as strength training activities for enhancing LBM.

A longitudinal assessment of change in VO2max and maximal heart rate in master athletes.

PURPOSE The purpose of this study was to determine the longitudinal change in VO2max and HRmax in male and female master endurance runners and to compare these changes based upon gender, age, and change in training volume. METHODS Eighty-six male (53.9 +/- 1.1 yr) and 49 female (49.1 +/- 1.2 yr) master endurance runners were tested an average of 8.5 yr apart. Subjects were grouped by age at first visit, change in VO2max, and change in training volume. Measurements included body composition by hydrostatic weighing, maximal exercise testing on a treadmill, and training history by questionnaire. Data were analyzed by ANOVA and multiple regression. RESULTS VO2max and HRmax declined significantly regardless of gender or age group (P < 0.05). The rate of change in VO2max by age group ranged from -1% to -4.6% per year for men and -0.5% to 2.4% per year for women. Men with the greatest loss in VO2max had the greatest loss in LBM (-2.8 +/- 0.7 kg), whereas women with the greatest loss in VO2max demonstrated the greatest change in training volume (-24.1 +/- 3.0 km.wk-1). Additionally, women with the greatest loss in VO2max (-9.6 +/- 2.6 mL.kg-1.min-1) did not replace estrogen after menopause independent of age. HRmax change did not differ by VO2max change or training volume change in either gender. CONCLUSIONS In conclusion, these data suggest that VO2max declines in male and female master athletes at a rate similar to or greater than that expected in sedentary older adults. Additionally, these data suggest that maintenance of LBM and VO2max were associated in men, whereas in women, estrogen replacement and maintenance of training volume were associated with maintained VO2max.

Eccentric muscle action increases site-specific osteogenic response.

PURPOSE Strain magnitude is known to be a primary determinant of the osteogenic response to loading. However, whether bone adaptation to muscle loading is determined primarily by load magnitude is unclear. The purpose of this study was to determine the contribution of load magnitude from muscle action on the site-specific osteogenic response. METHODS Twenty young women (12 exercise, 8 control) served as subjects. Bone mineral density (BMD) of the whole body and mid-femur segment and body composition were determined by dual-energy x-ray absorptiometry. Knee extension and flexion strengths were determined on a KinCom dynamometer, with surface electromyography of the vastus lateralis muscle. Exercise subjects trained three times weekly for 18 wk on a KinCom. One leg trained using eccentric knee extension and flexion, and the opposite leg trained using concentric knee extension and flexion. RESULTS Eccentric exercise demonstrated greater force production with lower integrated electromyographic signal (IEMG) compared with concentric exercise. Significant increases in muscle strength occurred in both exercised legs (P < 0.05), which were of similar relative change. However, only the eccentric trained leg significantly increased mid-femur segment BMD (+3.9%, P < 0.05) and mid-thigh segment lean mass (+5.2%, P < 0.05). CONCLUSIONS These results suggest that eccentric muscle training is more osteogenic than concentric muscle training and that eccentric training is more efficient by attaining higher force production with lower IEMG.

Endurance Training Delays Age of decline in Leg Strength and Muscle morphology

PURPOSE It has been reported that maximal strength peaks at approximately 30 yr of age, plateaus, and remains relatively stable for the next 20 yr, with an age-related decline in strength becoming significant after age 50. Much of the research attributes this decrease in peak force to age-associated reductions in muscle mass, with a selective atrophy and reduction in Type II fiber area and number being the primary factors. The influence that chronic endurance training has upon age-associated changes in muscular strength and muscle morphology has been largely undetermined. The purpose of this investigation was to examine the influence of chronic endurance training and age on leg extensor strength, and muscle fiber size and type distribution. METHODS Male master runners (N = 107, age range = 40-88 yr) were tested for maximal strength of the leg extensor muscles. A subgroup of 30 master athletes participated in muscle biopsy testing. The effects of age were addressed by subdividing the sample into five cohorts. RESULTS Peak isokinetic concentric torque did not differ between age groups until after age 70 yr. Regression analysis revealed a significant (P < 0.05, r(2) = 0.1838) age-associated decrease in relative strength (N.m.kg(-1) lean body mass). Type I and Type II fiber area and distribution did not differ between age groups through the eighth decade. CONCLUSIONS These data suggest that chronic endurance training can delay the age of significant decline in peak torque and changes in muscle morphology characteristics of the vastus lateralis.

An estimate of physical activity prevalence in a large population-based cohort.

PURPOSE The purpose of this study was to describe the prevalence of self-reported moderate and vigorous physical activity (PA) among 40,261 native Californians in relation to age, gender, education, race/ethnicity, and self-reported disease risk factors. METHODS Subjects, from the California Twin Program, completed a questionnaire that included three PA questions and were categorized by their level of PA: moderate and vigorous PA sufficient to meet CDC and ACSM guidelines. The relationship between demographic variables, chronic disease risk factors, and meeting the PA guidelines are reported. RESULTS For moderate and vigorous PA, 22.3% and 37.4% of the total group reported meeting the guidelines respectively. Approximately one-half of all subjects met either duration or frequency criteria, but not both, for moderate and vigorous PA. Only 11.2% and 27.4% reported no moderate or vigorous PA, respectively. Significant age and education gradients existed for both moderate and vigorous PA. An inverse association was noted between both moderate and vigorous PA guidelines and prevalence of chronic disease risk factors. Both frequency and duration of PA were required to adequately characterize the association between PA and health outcomes. CONCLUSIONS These data demonstrate 1) greater prevalence of sufficient moderate and vigorous PA and lower prevalence of sedentary behavior in this sample compared with adults nationwide, 2) a greater association between vigorous PA and improved health outcomes than was observed for moderate PA, 3) PA guidelines must focus on both frequency and duration of activity, and 4) age and education gradients in moderate and vigorous PA that could have implications for more effective targeting of guidelines to improve the PA prevalence of American adults.

Musculoskeletal adaptations to 16 weeks of eccentric progressive resistance training in young women.

We investigated the musculoskeletal adaptations and efficacy of a whole-body eccentric progressive resistance-training (PRT) protocol in young women. Subjects (n = 37; mean age, 24.3) were randomly assigned to one of 3 groups: high-intensity eccentric PRT (HRT), low-intensity eccentric PRT (LRT), or control. Subjects performed 3 sets of 6 repetitions at 125% intensity or 3 sets of 10 repetitions at 75% intensity in the HRT and LRT groups, respectively, 2 times per week for 16 weeks. Strength was determined by the concentric 1-repetition maximum (1RM) standard. Bone mass and body composition were measured by dual-energy x-ray absorptiometry (DXA). Blood and urine samples were obtained for deoxypyridinoline, osteocalcin, creatine kinase, and creatinine. Data were analyzed by repeated-measures analysis of variance with post hoc comparisons. Strength increased 20–40% in both training groups. Lean body mass increased in the LRT (0.7 ± 0.6 kg) and HRT (0.9 ± 0.9 kg) groups. Bone mineral content increased (0.855 ± 0.958 g) in the LRT group only. Deoxypyridinoline decreased and osteocalcin increased in the HRT and LRT groups, respectively. These findings suggest that submaximal eccentric training is optimal for musculoskeletal adaptations and that the intensity of eccentric training influences the early patterns of bone adaptation.

Longitudinal analysis of lactate threshold in male and female master athletes.

PURPOSE The lack of relationship between lactate threshold (LT) and running performance in older runners, and the increase in LT with age, has not been previously studied in a longitudinal design. We evaluated the cross-sectional and longitudinal changes in LT with age and compared the changes in LT with changes in performance variables. METHODS Fifty-one male and 23 female runners (39-77 yr) performed two graded treadmill exercise tests with minute-by-minute venous blood lactate analysis, separated by 5.8 +/- 1.6 yr (mean +/- SD). Body composition was determined by hydrodensitometry and training history by questionnaire. RESULTS There was no change in LBM over time, but significant decreases in [OV0312]O(2max) and training volume irrespective of age and gender (P < 0.05). LT as a percent of [OV0312]O(2max) increased with age (P < 0.05), demonstrated poor stability over time (r = 0.29, P = 0.01) compared with other parameters measured, and changes in LT were not related to changes in fitness or performance. CONCLUSION Based upon these findings, we conclude that the LT may be less precise than [OV0312]O(2max) or performance in the prescription of exercise intensities or as an evaluation tool in older individuals.

Sustainability of critical power determined by a 3-minute all-out test in elite cyclists.

McClave, SA, LeBlanc, M, and Hawkins, SA. Sustainability of critical power determined by a 3-minute all-out test in elite cyclists. J Strength Cond Res 25(11): 3093–3098, 2011—Critical power (CP) is a theoretical workload representative of an athletes maximal sustainable pace. Recent research has validated a 3-minute all-out test on a cycle ergometer for determining CP; however, few studies have investigated the sustainability of CP using this test. The purpose of this study was to determine the sustainability of CP established during the 3-minute test and the determinants of sustainability. A group of elite cyclists (N = 21) performed a &OV0312;O2max test, 3-minute all-out test, and a time to exhaustion (TTE) trial at CP on 3 different days separated by at least 24 hours. Expired gases were collected during all trials and analyzed for &OV0312;O2 and VCO2. Heart rate was measured by telemetry. Multiple regression was used to determine predictors of sustainability with significance predetermined at p < 0.05. &OV0312;O2max was measured at 58.9 ± 5.6 ml·kg−1·min−1, ventilation breakpoint at 44.9 ± 5.7 ml·kg−1·min−1 (75% &OV0312;O2max), and maximum heart rate at 179 ± 10 b·min−1. Peak power (PP) in the 3-minute all-out test was measured at 738 ± 170 W, and CP was determined at 305 ± 32 W or 79% of &OV0312;O2max. The &OV0312;O2 at CP was 55.4 ± 6.9 ml·kg−1·min−1, representing 94% of measured &OV0312;O2max. The mean TTE at CP was 14.79 ± 8.38 minutes. The difference score of PP − CP significantly predicted TTE (r = 0.65, p < 0.05). No other measured variables contributed to this prediction. Based on sustainability, these data suggest that the 3-minute all-out test may overestimate CP in elite cyclists, which could lead to overtraining if CP determined with this test is used to identify training intensities.

CHO-induced blunting of cortisol response to weightlifting exercise in resistance-trained older men

With weightlifting exercise, the attenuation of the cortisol response is a major factor by which an increase in muscle mass occurs. A reduction in the exercise-induced cortisol response has been observed in younger but not older men, suggesting that under normal circumstances older men may lack the mechanism(s) to down-regulate cortisol activity. The purpose of this study was to determine if CHO consumption during a weightlifting exercise bout could modify the cortisol response to exercise. Five resistance-trained older men (62.8 ± 1.5 y) completed (on 2 occasions) a 9-station weightlifting protocol (3 sets, 10 repetitions, 75% of 1RM). One session included the ingestion of a placebo beverage, and the other, a CHO solution. Blood samples were collected prior to, during, and after the exercise bout. With the placebo, plasma glucose levels remained unchanged, while plasma cortisol levels were significantly elevated (from 284 ± 49.7 nmol/L to 474 ± 130 nmol/L). In contrast, CHO consumption resulted in significantly higher plasma glucose levels (from 5.55 ± .48 to 7.63 ± 0.53 mmol) and a blunted cortisol response. These findings indi-cate that the stimulatory effect of exercise on cortisol secretion can be overcome by CHO administration.

ABSOLUTE LACTATE THRESHOLD PREDICTS ENDURANCE PERFORMANCE IN MASTER ATHLETES

In master athletes the relationship between lactate threshold (LT) and endurance performance is unclear, possibly due to age-related decrease in VO2peak. To determine whether an absolute measure of LT was a significant predictor of 10km running performance in master athletes, 51 men master athletes (40-77 yrs) performed a treadmill graded exercise test with minute-by-minute venous blood samples for lactate analysis. Training status and recent 10 km performances were determined by questionnaire. VO2peak (r=-0.56, P<0.001) and the two absolute measures of LT, Power at LT (r=-0.44, P<0.001) and VO2 at LT (r=-0.39, P=0.002), were significantly correlated to 10 km performance, but relative LT (% of VO2peak) was not (r=0.10, P=0.48). VO2peak (R 2 =0.31, P<0.001) and Power at LT (∆R 2 =0.08, P=0.015) were significant predictors of 10 km performance. These findings suggest that absolute LT is predictive of endurance performance in master athletes. Furthermore, relative LT is not a useful evaluation of LT in master athletes, possibly because of the age-related decrease in VO2peak. (Biol.Sport 26:105-112, 2009)