N. L. Jones

Randomised controlled trial of weightlifting exercise in patients with chronic airflow limitation.

BACKGROUND PATIENTS: with chronic airflow obstruction are often limited by muscle fatigue and weakness. As exercise rehabilitation programmes have produced modest improvements at best a study was designed to determine whether specific muscle training techniques are helpful. METHODS: Thirty four patients with chronic airflow limitation (forced expiratory volume in one second (FEV1) 38% of predicted values) were stratified for FEV1 to vital capacity (VC) ratio less than 40% and arterial oxygen desaturation during exercise and randomised to a control or weightlifting training group. In the experimental group training was prescribed for upper and lower limb muscles as a percentage of the maximum weight that could be lifted once only. It was carried out three times a week for eight weeks. RESULTS: Three subjects dropped out of each group; results in the remaining 14 patients in each group were analysed. Adherence in the training group was 90%. In the trained subjects muscle strength and endurance time during cycling at 80% of maximum power output increased by 73% from 518 (SE69) to 898 (95) s, with control subjects showing no change (506 (86) s before training and 479 (89) s after training). No significant changes in maximum cycle ergometer exercise capacity or distance walked in six minutes were found in either group. Responses to a chronic respiratory questionnaire showed significant improvements in dyspnoea and mastery of daily living activities in the trained group. CONCLUSIONS: Weightlifting training may be successfully used in patients with chronic airflow limitation, with benefits in muscle strength, exercise endurance, and subjective responses to some of the demands of daily living.

Short-term training increases human muscle MCT1 and femoral venous lactate in relation to muscle lactate

We examined the effects of increasing a known lactate transporter protein, monocarboxylate transporter 1 (MCT1), on lactate extrusion from human skeletal muscle during exercise. Before and after short-term bicycle ergometry training [2 h/day, 7 days at 65% maximal oxygen consumption (V˙o 2 max)], subjects ( n = 7) completed a continuous bicycle ergometer ride at 30%V˙o 2 max (15 min), 60%V˙o 2 max (15 min), and 75% V˙o 2 max (15 min). Muscle biopsy samples (vastus lateralis) and arterial and femoral venous blood samples were obtained before exercise and at the end of each workload. After 7 days of training the MCT1 content in muscle was increased (+18%; P < 0.05). The concentrations of both muscle lactate and femoral venous lactate were reduced during exercise ( P < 0.05) that was performed after training. High correlations were observed between muscle lactate and venous lactate before training ( r = 0.92, P < 0.05) and after training ( r = 0.85, P < 0.05), but the slopes of the regression lines between these variables differed markedly. Before training, the slope was 0.12 ± 0.01 mM lactate ⋅ mmol lactate-1 ⋅ kg muscle dry wt-1, and this was increased by 33% after training to 0.18 ± 0.02 mM lactate ⋅ mmol lactate-1 ⋅ kg muscle dry wt-1. This indicated that after training the femoral venous lactate concentrations were increased for a given amount of muscle lactate. These results suggest that lactate extrusion from exercising muscles is increased after training, and this may be associated with the increase in skeletal muscle MCT1.We examined the effects of increasing a known lactate transporter protein, monocarboxylate transporter 1 (MCT1), on lactate extrusion from human skeletal muscle during exercise. Before and after short-term bicycle ergometry training [2 h/day, 7 days at 65% maximal oxygen consumption (VO2max)], subjects (n = 7) completed a continuous bicycle ergometer ride at 30% VO2max (15 min), 60% VO2max (15 min), and 75% VO2max (15 min). Muscle biopsy samples (vastus lateralis) and arterial and femoral venous blood samples were obtained before exercise and at the end of each workload. After 7 days of training the MCT1 content in muscle was increased (+18%; P < 0.05). The concentrations of both muscle lactate and femoral venous lactate were reduced during exercise (P < 0.05) that was performed after training. High correlations were observed between muscle lactate and venous lactate before training (r = 0.92, P < 0.05) and after training (r = 0.85, P < 0.05), but the slopes of the regression lines between these variables differed markedly. Before training, the slope was 0.12 +/- 0.01 mM lactate.mmol lactate-1.kg muscle dry wt-1, and this was increased by 33% after training to 0.18 +/- 0.02 mM lactate.mmol lactate-1.kg muscle dry wt-1. This indicated that after training the femoral venous lactate concentrations were increased for a given amount of muscle lactate. These results suggest that lactate extrusion from exercising muscles is increased after training, and this may be associated with the increase in skeletal muscle MCT1.

Reasons for dropout from exercise programs in post-coronary patients.

The dropout rate in the 7-yr Ontario Exercise Heart Collaborative Study of post-coronary men engaged in exercise programs was examined in order to determine possible contributing factors. A questionnaire pertaining to psychosocial and program-related variables was distributed to 728 subjects who were previously assigned randomly on the basis of four prognostic risk factors (occupation, personality, hypertension, and angina) into exercise groups: low intensity exercise (LIE), and high intensity exercise (HIE). Comparisons of answers by the 639 respondents (266 dropouts; 373 compliers) were made initially by chi-square analysis to determine significant categories of questions and, subsequently, by a logistic transform to determine the specific questions which related significantly to the dropout rate. It was found that three main categories were associated with a high dropout rate: convenience aspects of the exercise center, perceptions of the exercise program, and family/lifestyle factors. These three main categories should be carefully considered when designing and implementing potential compliance-improving strategies for secondary prevention exercise programs entailing long-term adherence.

Regulation of skeletal muscle glycogen phosphorylase and PDH at varying exercise power outputs

This study investigated the transformational and posttransformational control of skeletal muscle glycogen phosphorylase and pyruvate dehydrogenase (PDH) at three exercise power outputs [35, 65, and 90% of maximal oxygen uptake (VO2 max)]. Seven untrained subjects cycled at one power output for 10 min on three separate occasions, with muscle biopsies at rest and 1 and 10 min of exercise. Glycogen phosphorylase in the more active (a) form was not significantly different at any time across power outputs (21. 4-29.6%), with the exception of 90%, where it fell significantly to 15.3% at 10 min. PDH transformation increased significantly from rest (average 0.53 mmol . kg wet muscle-1 . min-1) to 1 min of exercise as a function of power output (1.60 +/- 0.26, 2.77 +/- 0.29, and 3.33 +/- 0.31 mmol . kg wet muscle-1 . min-1 at 35, 65, and 90%, respectively) with a further significant increase at 10 min (4.45 +/- 0.35) at 90% VO2 max. Muscle lactate, acetyl-CoA, acetylcarnitine, and free ADP, AMP, and Pi were unchanged from rest at 35% VO2 max but rose significantly at 65 and 90%, with accumulations at 90% being significantly higher than 65%. The results of this study indicate that glycogen phosphorylase transformation is independent of increasing power outputs, despite increasing glycogenolytic flux, suggesting that flux through glycogen phosphorylase is matched to the demand for energy by posttransformational factors, such as free Pi and AMP. Conversely, PDH transformation is directly related to the increasing power output and the calculated flux through the enzyme. The rise in PDH transformation is likely due to increased Ca2+ concentration and/or increased pyruvate. These results demonstrate that metabolic signals related to contraction and the energy state of the cell are sensitive to the exercise intensity and coordinate the increase in carbohydrate use with increasing power output.

Arm cranking and wheelchair ergometry in elite spinal cord-injured athletes.

ABSTRACTWe investigated the cardiorespiratory responses to progressive incremental arm cranking (AC) and wheelchair ergometry (WCE) and upper limb strength in 72 elite male (N=61) and female (N=11) physically disabled athletes. Peak Vo2 in the two tests increased progressively in athletes categorize

Predictors of Health-related Quality of Life With Cardiac Rehabilitation After Acute Myocardial Infarction

BACKGROUND Health-related quality of life (HRQL) instruments provide valid and responsive outcome measures to assess the impact of disease and the response to interventions. However, they have not been applied widely to studies of rehabilitation after myocardial infarction. PURPOSE To examine the extent to which baseline sociodemographic and clinical characteristics predict baseline and change in generic and specific HRQL. METHODS A randomized controlled trial of an 8-week cardiac rehabilitation intervention or usual care, with follow-up for 12 months, in 201 patients with acute myocardial infarction (MI). Multiple regression analysis was used to identify predictors of HRQL. RESULTS Specific HRQL scores and exercise tolerance improved significantly more in rehabilitation patients than usual care patients by the end of the 8-week intervention. All HRQL measures and exercise tolerance in both groups improved significantly during the 12 month follow-up period but the differences between the groups were trivial. A poor baseline HRQL was the predominant predictor of improved generic and specific HRQL. Furthermore, greater improvement in HRQL consistently was associated with lower levels of cardiovascular risks such as absence of a previous MI or coronary artery bypass surgery, absence of angina, less smoking, and higher exercise tolerance. CONCLUSIONS Improved generic and specific HRQL was associated with poorer baseline HRQL and less baseline cardiovascular risk. This reinforces the importance of addressing health behavior changes as soon as possible after MI and the usefulness of assessing both generic and specific HRQL in evaluating treatment effectiveness.

Effects of short-term submaximal training in humans on muscle metabolism in exercise

Muscle metabolism, including the role of pyruvate dehydrogenase (PDH) in muscle lactate (Lac-) production, was examined during incremental exercise before and after 7 days of submaximal training on a cycle ergometer [2 h daily at 60% peak O2 uptake (V˙o 2 max)]. Subjects were studied at rest and during continuous steady-state cycling at three stages (15 min each): 30, 65, and 75% of the pretraining V˙o 2 max. Blood was sampled from brachial artery and femoral vein, and leg blood flow was measured by thermodilution. Biopsies of the vastus lateralis were obtained at rest and during steady-state exercise at the end of each stage. V˙o 2 max, leg O2 uptake, and the maximum activities of citrate synthase and PDH were not altered by training; muscle glycogen concentration was higher. During rest and cycling at 30% V˙o 2 max, muscle Lac- concentration ([Lac-]) and leg efflux were similar. At 65%V˙o 2 max, muscle [Lac-] was lower (11.9 ± 3.2 vs. 20.0 ± 5.8 mmol/kg dry wt) and Lac- efflux was less [-0.22 ± 0.24 (one leg) vs. 1.42 ± 0.33 mmol/min] after training. Similarly, at 75%V˙o 2 max, lower muscle [Lac-] (17.2 ± 4.4 vs. 45.2 ± 6.6 mmol/kg dry wt) accompanied less release (0.41 ± 0.53 vs. 1.32 ± 0.65 mmol/min) after training. PDH in its active form (PDHa) was not different between conditions. Calculated pyruvate production at 75%V˙o 2 max fell by 33%, pyruvate reduction to lactate fell by 59%, and pyruvate oxidation fell by 24% compared with before training. Muscle contents of coenzyme A and phosphocreatine were higher during exercise after training. Lower muscle lactate production after training resulted from improved matching of glycolytic and PDHafluxes, independently of changes in muscle O2 consumption, and was associated with greater phosphorylation potential.Muscle metabolism, including the role of pyruvate dehydrogenase (PDH) in muscle lactate (Lac-) production, was examined during incremental exercise before and after 7 days of submaximal training on a cycle ergometer [2 h daily at 60% peak O2 uptake (VO2 max)]. Subjects were studied at rest and during continuous steady-state cycling at three stages (15 min each): 30, 65, and 75% of the pretraining VO2 max. Blood was sampled from brachial artery and femoral vein, and leg blood flow was measured by thermodilution. Biopsies of the vastus lateralis were obtained at rest and during steady-state exercise at the end of each stage. VO2 max, leg O2 uptake, and the maximum activities of citrate synthase and PDH were not altered by training; muscle glycogen concentration was higher. During rest and cycling at 30% VO2 max, muscle Lac- concentration ([Lac-]) and leg efflux were similar. At 65% VO2 max, muscle [Lac-] was lower (11.9 +/- 3.2 vs. 20.0 +/- 5.8 mmol/kg dry wt) and Lac- efflux was less [-0.22 +/- 0.24 (one leg) vs. 1.42 +/- 0.33 mmol/min] after training. Similarly, at 75% VO2 max, lower muscle [Lac-] (17.2 +/- 4.4 vs. 45.2 +/- 6.6 mmol/kg dry wt) accompanied less release (0.41 +/- 0.53 vs. 1.32 +/- 0.65 mmol/min) after training. PDH in its active form (PDHa) was not different between conditions. Calculated pyruvate production at 75% VO2 max fell by 33%, pyruvate reduction to lactate fell by 59%, and pyruvate oxidation fell by 24% compared with before training. Muscle contents of coenzyme A and phosphocreatine were higher during exercise after training. Lower muscle lactate production after training resulted from improved matching of glycolytic and PDHa fluxes, independently of changes in muscle O2 consumption, and was associated with greater phosphorylation potential.

Relation of exercise to the recurrence rate of myocardial infarction in men: Ontario exercise-heart collaborative study

The Ontario Exercise-Heart Collaborative Study was a multicenter randomized clinical trial of high Intensity exercise for the prevention of recurrent myocardial infarction in men. The 4-year recurrence rate among 379 patients on a program of high intensity exercise did not differ significantly from that among 354 control patients on a program of light exercise, despite the greater reduction in heart rate in the former group. The relative odds of recurrence in the high intensity group were 1.09, with 95% confidence limits of 0.61 and 1.96.

Predictors of dropout from cardiac exercise rehabilitation: Ontario exercise-heart collaborative study*

The Ontario Exercise-Heart Collaborative Study was a multicenter randomized clinical trial of high intensity exercise for the prevention of recurrent myocardial infarction in 733 men. Of the 678 subjects who could have participated for at least 3 years, 315 (46.5%) dropped out. Stepwise multiple linear logistic regression analysis was carried out to examine the relation between subject characteristics and the probability of dropping out during the study. Analysis was performed on the entry group as a whole by considering those subjects who had reinfarction while complying with the program and also by excluding all subjects with reinfarctions. The consistent and statistically significant predictors of dropout in both analyses were smoking and a blue collar occupation. Angina was significantly associated with dropout only when reinfarctions were excluded. It may be important to consider these factors when investigating the potential for compliance-improving strategies in reducing dropout from exercise rehabilitation programs.

Effects of short-term training on plasma acid-base balance during incremental exercise in man

The present study examined the effect of short‐term submaximal training on plasma acid‐base balance during exercise. The influence of water and ion exchange between plasma, active muscles and erythrocytes in the response to training were also studied. The contributions of independent physicochemical variables (i.e. strong ion difference ([SID]), total concentration of weak acids ([Atot]) and PO2) to changes in arterial (a) and femoral venous (v) plasma [H+] were examined in six subjects (age 24 ± 1.5 years; maximum oxygen consumption rate (V̇O2,max), 3.67 ± 0.24 l min−1) during steady‐state cycling for 15 min at each of 30, 65 and 75 % of V̇O2,max before (pre) and after (post) training for 7 days on a cycle ergometer (2 h daily at 60 % V̇O2,max). The rise in [H+]a during exercise was attenuated post‐training by 3 and 5 nequiv l−1 (P < 0.05) at 65 and 75 % V̇O2,max, respectively, due first to less decrease in [SID]a, secondary to lower [Cl−]a and [Lac−]a; and second, to a reduction in [Atot]a, due to greater plasma volume and less plasma water flux (Jv) into leg muscle (P < 0.05). The rise in [H+]v was also less in post‐training by 4.5 and 6 nequiv l−1 (P < 0.05) at 65 and 75 % V̇O2,max, respectively, and attributed solely to lower [Atot]v (P < 0.05). Attenuation of exercise induced decreases in plasma [SID]a and [SID]v from rest to 75 % V̇O2,max was accompanied by reductions in erythrocyte Lac− and Cl− uptake (P < 0.05), and smaller increases in erythrocyte K+ release (P < 0.05). We conclude that the training‐induced attenuation of the rise in plasma [H+]a and [H+]v during incremental exercise resulted from adaptive changes within muscles (less Lac− production and less water uptake) and erythrocytes (less uptake of Lac−, Cl− and K+), leading to greater [SID] and lower [Atot] in both arterial and femoral venous plasma.