Donald H. Paterson

Physical activity and functional limitations in older adults: a systematic review related to Canada's Physical Activity Guidelines.

BackgroundThe purpose was to conduct systematic reviews of the relationship between physical activity of healthy community-dwelling older (>65 years) adults and outcomes of functional limitations, disability, or loss of independence.MethodsProspective cohort studies with an outcome related to functional independence or to cognitive function were searched, as well as exercise training interventions that reported a functional outcome. Electronic database search strategies were used to identify citations which were screened (title and abstract) for inclusion. Included articles were reviewed to complete standardized data extraction tables, and assess study quality. An established system of assessing the level and grade of evidence for recommendations was employed.ResultsSixty-six studies met inclusion criteria for the relationship between physical activity and functional independence, and 34 were included with a cognitive function outcome. Greater physical activity of an aerobic nature (categorized by a variety of methods) was associated with higher functional status (expressed by a host of outcome measures) in older age. For functional independence, moderate (and high) levels of physical activity appeared effective in conferring a reduced risk (odds ratio ~0.5) of functional limitations or disability. Limitation in higher level performance outcomes was reduced (odds ratio ~0.5) with vigorous (or high) activity with an apparent dose-response of moderate through to high activity. Exercise training interventions (including aerobic and resistance) of older adults showed improvement in physiological and functional measures, and suggestion of longer-term reduction in incidence of mobility disability. A relatively high level of physical activity was related to better cognitive function and reduced risk of developing dementia; however, there were mixed results of the effects of exercise interventions on cognitive function indices.ConclusionsThere is a consistency of findings across studies and a range of outcome measures related to functional independence; regular aerobic activity and short-term exercise programmes confer a reduced risk of functional limitations and disability in older age. Although a precise characterization of a minimal or effective physical activity dose to maintain functional independence is difficult, it appears moderate to higher levels of activity are effective and there may be a threshold of at least moderate activity for significant outcomes.

Age-related changes in speed of walking

Self-paced walking was used as a measure of the neuromuscular slowing observed with aging. The effects of age on the choice of speed of walking, stride length, and step frequency were described for 289 males and 149 females aged 19 to 102 yr. These subjects were asked to walk at three self-selected paces (slow, normal, and fast) over an 80-m indoor course. Sixty-two years coincided with an accelerated decline in speed of walking. Before 62 yr, there was a 1 to 2% per decade decline in normal walking speed. After 63 yr, females showed a 12.4% per decade decrease and males showed a 16.1% per decade decrease. The eldest group (63 yr and older) had a significantly slower speed of walking and smaller step length than the younger groups (19 to 39 and 40 to 62 yr) for all paces. Heart rate at the three paces was not changed across age. In a multiple regression analysis, the only significant independent variable for walking speed at all three paces was (age), which accounted for 19 to 38% of the variance. When the population was divided into two age ranges (19 to 62 and 63 to 102 yr), walking speed was associated with height before 62 yr and with height and age after 62 yr.

Can primary care doctors prescribe exercise to improve fitness?: The step test exercise prescription (STEP) project

BACKGROUND Sedentary lifestyle is associated with adverse health outcomes. Available evidence suggests that, despite positive attitudes toward regular exercise in promoting a healthy lifestyle, few physicians actually prescribe exercise for their patients. Barriers include lack of skills and standard office instruments. Because primary care physicians have regular contact with a large proportion of the population, the impact of preventive health interventions may be great. OBJECTIVES To determine the effect of an exercise prescription instrument (i.e., Step Test Exercise Prescription [STEP]), compared to usual-care exercise counseling delivered by primary care doctors on fitness and exercise self-efficacy among elderly community-dwelling patients. DESIGN Randomized controlled trial; baseline assessment and intervention delivery with postintervention follow-up at 3, 6, and 12 months. SETTING Four large (>5000 active patient files) academic, primary care practices: three in urban settings and one in a rural setting, each with four primary care physicians; two clinics provided the STEP intervention and two provided usual care control. PARTICIPANTS A total of 284 healthy community-dwelling patients (72 per clinic) aged >65 years were recruited in 1998-1999. INTERVENTION STEP included exercise counseling and prescription of an exercise training heart rate. MAIN OUTCOME MEASURES The primary outcome measure was aerobic fitness (VO(2max)). Secondary outcomes included predicted VO(2max) from the STEP test, exercise self-efficacy (ESE), and clinical anthropometric parameters. RESULTS A total of 241 subjects (131 intervention, 110 control) completed the trial. VO(2max) was significantly increased in the STEP intervention group (11%; 21.3 to 24ml/kg/min) compared to the control group (4%; 22 to 23ml/kg/min) over 6 months (p <0.001), and 14% (21.3 to 24.9ml/kg/min) and 3% (22.1 to 22.8ml/kg/min), respectively, at 12 months (p <0.001). A similar significant increase in ESE (32%; 4.6 vs 6.8) was observed for the STEP group compared to the control group (22%; 4.2 vs 5.4) at 12 months (p < 0.001). Systolic blood pressure decreased 7.3% and body mass index decreased 7.4% in the STEP group, with no significant change in the control group (p <0.05). Exercise counseling time was significantly (p <0.02) longer in the STEP (11.7+/-3.0 min) compared to the control group (7.1+/-7.0 min), but more (p <0.05) subjects completed > or =80% of available exercise opportunities in the STEP group. CONCLUSIONS Primary care physicians can improve fitness and exercise confidence of their elderly patients using a tailored exercise prescription (e.g., STEP). Further, STEP appears to maintain benefits to 12 months and may improve exercise adherence. Future study should determine the impact of combining cognitive/behavior change strategies with STEP.

Exercise on-transient gas exchange kinetics are slowed as a function of age.

The purpose was to characterize gas exchange kinetics following the on-transient of exercise in men aged 30-80 yr. Forty-six men completed square wave exercise tests from loadless cycling to subventilatory threshold (V(E)T) work rates with gas exchange measured breath-by-breath. Signal averaged data were fit with a monoexponential equation to derive time constants (tau) for gas exchange and ventilation (tau VO2, tau VCO2, tau VE) and heart rate (tau HR). There was a significant slowing of ventilation and gas exchange kinetics across age with linear regression yielding an increase of 0.67 s.yr-1 for tau VO2 (39 s in young to 61 s in old), 0.57 s.yr-1 for tau VCO2, and 0.65 s.yr-1 for tau VE, whereas tau HR (44 to 41 s) was not changed significantly. The slowed VO2 kinetics with age may reflect limitations in muscle blood flow or in control of the rate of oxidative metabolism. The less marked slowing of tau VCO2 compared with tau VO2 across age may reflect reduced CO2 storage capacity with loss of muscle tissue. The tau VE change across age was similar to that for tau VCO2 (tau VE/tau VCO2 unchanged). The present study demonstrated marked age-related slowing of gas exchange dynamics at exercise onset.

Longitudinal study of determinants of dependence in an elderly population.

Objectives: To describe those factors, from the host of initial measures in ambulatory, independent older men and women, that were determinants of becoming dependent over an 8‐year follow‐up.

Effects of aerobic endurance training on gas exchange kinetics of older men

The kinetics of gas exchange at the on-transient of exercise are appreciably slowed in older individuals. Eight older men (72 yr) completed 6 months of aerobic cycle training. Ventilation and gas exchange kinetics were determined at the onset of a below threshold (ventilatory threshold, V(E)T) square wave exercise function and compared with control values (N = 4, age 70 yr). Gas exchange data were measured breath-by-breath and signal averaged data were fit with a monoexponential function to determine the time constants (tau). The training group showed significant increases in VO2max (20%) and VO2 at V(E)T (21%). The tau for oxygen uptake kinetics decreased significantly (62.2 +/- 15.5 to 31.9 +/- 7.0 s). The tau VCO2 (70.9 +/- 10.9 to 43.8 +/- 11.4 s) and tau VE (89.2 +/- 18.0 to 50.4 +/- 11.3) also were significantly faster posttraining; however, tau HR (38.1 +/- 20.5 to 28.6 +/- 7.2) was not significantly altered. Thus, with a vigorous training program, the kinetics of gas exchange of older individuals were faster, and approached values reported in fit young subjects.

Prior heavy exercise elevates pyruvate dehydrogenase activity and speeds O2 uptake kinetics during subsequent moderate‐intensity exercise in healthy young adults

The adaptation of pulmonary oxygen uptake during the transition to moderate‐intensity exercise (Mod) is faster following a prior bout of heavy‐intensity exercise. In the present study we examined the activation of pyruvate dehydrogenase (PDHa) during Mod both with and without prior heavy‐intensity exercise. Subjects (n= 9) performed a Mod1–heavy‐intensity–Mod2 exercise protocol preceded by 20 W baseline. Breath‐by‐breath kinetics and near‐infrared spectroscopy‐derived muscle oxygenation were measured continuously, and muscle biopsy samples were taken at specific times during the transition to Mod. In Mod1, PDHa increased from baseline (1.08 ± 0.2 mmol min−1 (kg wet wt)−1) to 30 s (2.05 ± 0.2 mmol min−1 (kg wet wt)−1), with no additional change at 6 min exercise (2.07 ± 0.3 mmol min−1 (kg wet wt)−1). In Mod2, PDHa was already elevated at baseline (1.88 ± 0.3 mmol min−1 (kg wet wt)−1) and was greater than in Mod1, and did not change at 30 s (1.96 ± 0.2 mmol min−1 (kg wet wt)−1) but increased at 6 min exercise (2.70 ± 0.3 mmol min−1 (kg wet wt)−1). The time constant of was lower in Mod2 (19 ± 2 s) than Mod1 (24 ± 3 s). Phosphocreatine (PCr) breakdown from baseline to 30 s was greater (P < 0.05) in Mod1 (13.6 ± 6.7 mmol (kg dry wt)−1) than Mod2 (6.5 ± 6.2 mmol (kg dry wt)−1) but total PCr breakdown was similar between conditions (Mod1, 14.8 ± 7.4 mmol (kg dry wt)−1; Mod2, 20.1 ± 8.0 mmol (kg dry wt)−1). Both oxyhaemoglobin and total haemoglobin were elevated prior to and throughout Mod2 compared with Mod1. In conclusion, the greater PDHa at baseline prior to Mod2 compared with Mod1 may have contributed in part to the faster kinetics in Mod2. That oxyhaemoglobin and total haemoglobin were elevated prior to Mod2 suggests that greater muscle perfusion may also have contributed to the observed faster kinetics. These findings are consistent with metabolic inertia, via delayed activation of PDH, in part limiting the adaptation of pulmonary and muscle O2 consumption during the normal transition to exercise.

OXYGEN UPTAKE KINETICS OF OLDER HUMANS ARE SLOWED WITH AGE BUT ARE UNAFFECTED BY HYPEROXIA

Cross‐sectional studies have compared the oxygen uptake (VO2) kinetics during the on‐transient of moderate intensity exercise in older and younger adults. The slower values in the older adults may have been due to an age‐related reduction in the capacity for O2 transport or alternatively a reduced intramuscular oxidative capacity. We studied: (1) the effects of ageing on VO2 kinetics in older adults on two occasions 9 years apart, and (2) the effect of hyperoxia on VO2 kinetics at the second test time. After a 9 year period, follow‐up testing was undertaken on seven older adults (78 ± 5 years, mean ±s.d.). They each performed six repeats of 6 min bouts of constant‐load cycle exercise from loadless cycling to 80 % of their ventilatory threshold. They breathed one of two gas mixtures (euoxia: inspired O2 fraction, FI,O2, 0·21; hyperoxia: FI,O2, 0·70) on different trials determined on a random basis. Breath‐by‐breath VO2 data were time aligned and ensemble averaged. VO2 kinetics, modelled with a single exponential from phase 2 onset (+20 s) to steady state and described by the exponential time constant ([tau]) were compared with data collected from the same adults 9 years earlier. One‐way repeated measures analysis of variance revealed that [tau] was slowed significantly with age (from 30 ± 8 to 46 ± 10 s), but was unaffected by hyperoxia (43 ± 15 s). We concluded that: (1) in older adults studied longitudinally over a 9 year period, the on‐transient VO2 kinetics are slowed, in agreement with, but to a greater extent, than from cross‐sectional data; and (2) the phase 2 time constant ([tau]) for these older adults was not accelerated by hyperoxic breathing. Thus the expected hyperoxia‐induced increase in the capacity for O2 transport was not associated with faster on‐transient VO2 kinetics suggesting either that O2 transport may not limit VO2 kinetics during the 8th decade, or that O2 transport was not improved with hyperoxia.

The effect of hypoxia on pulmonary O2 uptake, leg blood flow and muscle deoxygenation during single-leg knee-extension exercise.

The effect of hypoxic breathing on pulmonary O2 uptake (VO2p), leg blood flow (LBF) and O2 delivery and deoxygenation of the vastus lateralis muscle was examined during constant‐load single‐leg knee‐extension exercise. Seven subjects (24 ± 4 years; mean ±s.d.) performed two transitions from unloaded to moderate‐intensity exercise (21 W) under normoxic and hypoxic (PETO2= 60 mmHg) conditions. Breath‐by‐breath VO2p and beat‐by‐beat femoral artery mean blood velocity (MBV) were measured by mass spectrometer and volume turbine and Doppler ultrasound (VingMed, CFM 750), respectively. Deoxy‐(HHb), oxy‐, and total haemoglobin/myoglobin were measured continuously by near‐infrared spectroscopy (NIRS; Hamamatsu NIRO‐300). VO2p data were filtered and averaged to 5 s bins at 20, 40, 60, 120, 180 and 300 s. MBV data were filtered and averaged to 2 s bins (1 contraction cycle). LBF was calculated for each contraction cycle and averaged to 5 s bins at 20, 40, 60, 120, 180 and 300 s. VO2p was significantly lower in hypoxia throughout the period of 20, 40, 60 and 120 s of the exercise on‐transient. LBF (l min−1) was approximately 35% higher (P > 0.05) in hypoxia during the on‐transient and steady‐state of KE exercise, resulting in a similar leg O2 delivery in hypoxia and normoxia. Local muscle deoxygenation (HHb) was similar in hypoxia and normoxia. These results suggest that factors other than O2 delivery, possibly the diffusion of O2, were responsible for the lower O2 uptake during the exercise on‐transient in hypoxia.

Determinants of oxygen uptake kinetics in older humans following single-limb endurance exercise training.

We hypothesised that the observed acceleration in the kinetics of exercise on‐transient oxygen uptake (V̇O2) of five older humans (77 ± 7 years (mean ± S.D.) following 9 weeks of single‐leg endurance exercise training was due to adaptations at the level of the muscle cell. Prior to, and following training, subjects performed constant‐load single‐limb knee extension exercise. Following training V̇O2 kinetics (phase 2, τ) were accelerated in the trained leg (week 0, 92 ± 44 s; week 9, 48 ± 22 s) and unchanged in the untrained leg (week 0, 104 ± 43 s; week 9, 126 ± 35 s). The kinetics of mean blood velocity in the femoral artery were faster than the kinetics of V̇O2, but were unchanged in both the trained (week 0, 19 ± 10 s; week 9, 26 ± 11 s) and untrained leg (week 0, 20 ± 18 s; week 9, 18 ± 10 s). Maximal citrate synthase activity, measured from biopsies of the vastus lateralis muscle, increased (P < 0.05) in the trained leg (week 0, 6.7 ± 2.0 μmol (g wet wt)−1 min−1; week 9, 11.4 ± 3.6 μmol (g wet wt)−1 min−1) but was unchanged in the untrained leg (week 0, 5.9 ± 0.5 μmol (g wet wt)−1 min−1; week 9, 7.9 ± 1.9 μmol (g wet wt)−1 min−1). These data suggest that the acceleration of V̇O2 kinetics was due to an improved rate of O2 utilisation by the muscle, but was not a result of increased O2 delivery.