The aim of our investigation is to compare the mechanical efficiency of work and economy of movements in 14 – 15 and 16 – 17 years old road cyclists. Two years longer training experience in the older group of cyclists, as well as, process of growth of adolescent and young athletes can influence these characteristics. Twenty-four Latvian young road cyclists participated in the investigation. Every road cyclist performed an incremental load test on a mechanical bicycle ergometer (Monark, Sweden). An initial load intensity was 27 W, then it was increased step by step for 12 W every two minutes. A cardiopulmonary diagnostic equipment was used during the test to register an electrocardiogram and respiratory characteristics. An average value of the last load step minute of all characteristics is calculated. A lactic acid concentration in the capillary blood is detected by special lactate analysers. The lactic acid concentration in the capillary blood is determined every two minutes. Using the respiratory characteristics (exchange of gases) of oxygen uptake volume and volume of carbon dioxide expiration per minute, the respiratory quotient was determined. Thermal equivalents of oxygen for certain respiratory quotients values were taken from the table. Then we calculated an energy expenditure for every road cyclist at a certain workload (aerobic and anaerobic threshold levels loads). We calculated the amount of energy expenditure in percents used for mechanical work production on the bicycle ergometer (the workload determined in the test) from all energy expenditure. It was a mechanical efficiency of every road cyclist. Using the data of oxygen uptake and mechanical workload on the bicycle ergometer, we calculated the economy of movements of road cyclists at the aerobic and anaerobic thresholds load intensities. The average mechanical efficiency of bicycle ergometer work at the anaerobic threshold intensity load is significantly better in 16 – 17 years old athletes (21.6 ± 1.0 %) than in 14 – 15 years old cyclists (20.7 ± 0.7 %), p < 0.001. The relationship between the work mechanical efficiency on the bicycle ergometer and the power production is not determined, p > 0.005. The average economy of movements on bicycle ergometer is significantly greater in 16 – 17 years old cyclists (4.549 ± 0.204 kJ/ l) in comparision with 14 – 15 years old group (4.372 ± 0.164 kJ/ l), p<0,002. . The relationship between the economy of movements and the power production is not detected, p > 0.05. The differences between the work mechanical efficiency and economy of movements on bicycle ergometer average values are not significant in both age groups of the cyclists at the aerobic threshold intensity load. The relationship between the power production on bicycle ergometer and the work mechanical efficiency or economy of movements, respectively, is significant, p < 0.05. If the power produced on bicycle ergometer increases, the growth of the work mechanical efficiency and economy of movements is determined at low intensity aerobic exercises. The significant correlations between the aerobic capacity characteristic – oxygen uptake and the work mechanical efficiency or economy of movements are not determined, p > 0.05.