Despite no change in exercise economy, diet induced weight loss was associated with decreased heart rate during walking, stair climbing, and grade walking. Addition of exercise training during the diet induced weight loss did little to further decrease heart rate. However, during the year following the weight loss, inclusion of either aerobic or resistance training helped to maintain the decreased heart rate obtained during weight loss. Individuals who did not exercise train during the year following weight loss did not maintain the lower heart rate during locomotion. The aerobic trainers of course had enhanced aerobic fitness and the resistance trainers had enhanced strength. Taken together these data suggest that exercise training during and following weight loss has a positive affect on fitness that translates into increased ease (decreased heart rate) during locomotion one year following weight loss. Based on previous research this increased ease should translate into more free living (separate from exercise training) physical activity (7
) and in turn the increased physical activity should lead to reduced weight gain (3
Both aerobic and resistance training had an affect on maintaining the weight loss induced decrease in heart rate during locomotion. A number of investigations have shown that either resistance training (1
) or aerobic training (10
) are accompanied by reduced heart rate in submaximal walking and running. To our knowledge no studies have compared resistance and aerobic training effects on walking and stair climbing heart rate during and following a diet induced weight loss. Aerobic and resistance training had only minimal additional affects on heart rate response to walking and stair climbing immediately following weight loss. However, the exercise training did have a positive affect on reducing the heart rate during cycling immediately following weight loss.
During the walk, grade walk and stair climbing subjects were required to do less work following weight loss because of their reduced body mass (approximately 15% less). The no exercise group thus reduced their heart rates during these tasks, and may have masked any changes induced by the exercise training. During biking, work did not decrease as much during weight loss, i.e. the work on the bike ergometer remained at 50 W. The work done to move the legs during each pedal cycle was of course reduced after weight loss since presumably subjects would have lost some mass from the legs. However, the overall decrease in work would be minimal when compared to walking and stair climbing. Therefore the effects of the exercise training on heart rate response during work is more easily detected without reduced work of moving lower body mass confounding the analysis. Observation of the biking data supports this contention, with the no exercise group not changing heart rate while the combined aerobic and resistance training groups decreasing heart rate 9 beats/min following weight loss. Therefore it can be concluded that exercise training during weight loss has a positive affect on improving ease of exercise in an absolute task (such as cycling at 50 watts). However, exercise training during weight loss has less of an affect for tasks in which the work is being done to move reduced body weight.
Increased efficiency at low cycling intensity has been reported after weight loss (13
) but not at higher intensity exercise (5
). Consistent with studies that used higher intensity steady state exercise the present study did not find a difference in exercise economy for any of the moderate intensity submaximal exercise tasks following weight loss. Mechanisms for why exercise economy/efficiency increases at very low intensities, i.e. 25 W or less or equal to 2 METs) but not at more moderate, i.e. greater than 3 METs is unknown.
Consistent with the increase in biking efficiency found with low intensity exercise, RQ has been shown to decrease during low intensity (25 W and lower) biking (15
)), showing less carbohydrate metabolism. Because biking efficiency was also increased requiring less energy expenditure, presumably subjects would be able to perform the biking task with less activation of inefficient fast twitch muscle fibers that would be more dependent on carbohydrate metabolism. We observed no weight loss related decrease in RQ for our moderate intensity exercises (including cycling), except for the stair climb. On the other hand similar to Amati et al (Amati 2008) we observed a decrease in RQ during the walk and grade walk for the aerobic exercisers but not for the resistance trainers or non exercisers.
Although the aerobic and resistance training decreased heart rate during the submaximal tasks similarly, the mechanisms for the improvements are probably different. Improvements in aerobic fitness would be accompanied by increases in blood volume and increased maximal and submaximal stroke volume. Increased stroke volume would be expected to translate into reduced heart rate at rest and during submaximal exercise. Resistance training normally has little effect on aerobic capacity and maximal stroke volume. However, it does affect strength and increased strength is associated with a reduction in neural activation of muscle during submaximal tasks (6
). It could therefore be argued that stronger individuals will not have as great an activation of the sympathetic nervous system during standardized tasks such as walking or riding a stationary bicycle, i.e. a lower percent of maximal force will be needed to perform a standardized task so less relative muscle activation and less disturbance of homeostasis. Reduced neural-hormonal disturbance would then be accompanied by changes in extrinsic control of heart rhythm so that heart rate is reduced. Of course either stroke volume or arterial-venous differences would have to accompany the reduced heart rate if oxygen uptake remained the same as it did in this study. It is impossible to know from the present study whether submaximal stroke volume or arterial-venous differences occurred.
Exercise economy was not affected by weight loss or exercise training. However, heart rate and thus difficulty in walking, stair climbing and bicycling was reduced following weight loss. Although exercise training did not have an affect on exercise heart rate following weight loss, exercise training during the year following weight loss maintained reduced exercise heart rates obtained during weight loss. The results of this study, therefore, suggest that at least some moderately intense exercise training may be helpful in improving aerobic and strength fitness and ease of movement during and especially following weight loss. This strategy may be helpful in improving health and preventing or at least slowing weight regain since reduced heart rate and thus more ease in locomotion may translate into increased participation in free living physical activity (7
) and in turn improved body weight maintenance (3
). Although, not tested in this study it is probable that combined aerobic and resistance training may have an additive affect on improving ease of locomotion following weight loss.