Mechanical efficiency during different submaximal exercise intansities

Introduction

Mechanical efficiency of the movements is an important criterion for evaluating the relationship between energy input and resulting power output in exercise (McArdle et al., 1996). The aim of this study was to examine mechanical efficiency changes during submaximal exercises above anaerobic threshold and during standard steady-rate test applied as a pre-and post-test after exhaustive cycle ergometer load.

Methods

Mechanical efficiency (ME) of the movements was computed from three exercise test protocols performed on a bicycle ergometer. Subjects were 17 athletes (rowers and cyclists), 20-24 years of age, weight 77.87.06. Exercise protocols were: 1. Graded test to exhaution started at 60W, with 30W increments every 90 sec (60 revolution per minute). ME was calculated above the anaerobic threshold by Volkov, 1975 (at 120W, 210W) up to the power step when the respiratory exchange ratio (RER) equals to 1; 2. 5-minute standard ergometer test (2W. kg-1) was performed prior (T1) graded test and in 25th minutes the test (T2) was performed once again; 3. The same standard load (T1 and T2) was carried out prior and after 7-minute ergometer exercise with 3W.kg-1. ME in protocols 2 and 3 (based on those of Pavlova, 1981) was considered only for the 5-minute test (T1, T2). Pulmonary gas exchange (VO2, VCO2) was measured during the three protocols. RER, chemical energy expenditure, mechanical energy were calculated. ME was expressed in per cent by efficiency equation.

Results

ME during graded test increased from anaerobic threshold (VO2-2.10.14 l.min-1, VCO2-1.850.21 l. min-1, RER -0.880.1) until RER became 1. VO2 max of the group varied from 4.0l. min-1 to 5.5 l. min-1. ME changes in range of study were between 15 per cent and 23 per cent. The influence of graded test on ME of standard test (T2) was different. The energy cost of post aerobic steady-rate test (T2) comparing to T1 was decreased in some individuals corresponding with higher ME values. On the contrary in other subjects energy expenditure increased and ME dropped. The results of protocols were similar to those of previous protocol. ME changes were small but they indicated appreciably the recovery level of athletes in 25th minute after graded test and 7-minute ergometer cycling (60-75% VO2 max).

Discussion/Conclusion

The results of this study showed that the mechanical efficiency increased in accordance with the intensity of load until RER became 1. It wasn’t found dependence between the aerobic capacity (VO2 max) of subject and ME acceleration. Probably the athletes realized maximal oxygen uptake with different energy required for internal and external friction and efficiency of muscle fiber. Data of standard test pointed that its energy cost, respectively ME changed in dependence of actual metabolic and functional state of subject. In conclusion, the findings revealed individual distribution of aerobic produced energy for external work and energy lost as heat during submaximal intensities. ME of standard steady-rate load could be one of possible predictors for coming athlete performance.

References

[1]. Volkov N. (1975). Theor. Pract. Phys., 11, 28-36.
[2]. Pavlova E. (1981). Diss. Sofia, 55-81.
[3]. McArdle et al. (1996), Exer. Physiol., 167-232.