*3.3. Exercise Economy (*Δ*VO2/*Δ*Workload)*

Exercise economy is defined as the energy expenditure for given absolute exercise intensity and is expressed as VO2 at a given physical work or power output [4,24,40,41]. Remarkable economy means lower VO2 for given power output and is an advantage in endurance performance because it results in the utilisation of a lower percentage of

VO2max for particular exercise intensity. Low VO2max scores can even be compensated by remarkable economy [24].

The importance of exercise economy has been described in different athletes such as runners and soccer players [41,42], and the improvements could be achieved by endurance training through improved muscle oxidative capacity and changes in motor unit recruitment patterns. Researches support the effects of resistance and plyometric exercises and high-intensity interval training (HIIT) on exercise economy [40,41]. Reduction in submaximal VO2 is significantly correlated with the reduced minute ventilation (VE) and heart rate (HR) [24].

The slope of VO2 (mL/min) to workload (Watts) demonstrates the economy of exercise and represents an indirect measure of cardiac output and aerobically generated ATP [23]. Commonly there is a continual rise throughout the exercise with the average slope of 10 mL/min/W with all exercise data [11]. Figure 1 depicts the VO2/workload responses of two athletes with different exercise economy. To evaluate an athlete's exercise economy, it is better to measure it during an incremental test, which is fast enough to continually increase the VO2 similar to the intensities more commonly experienced during sports competition and at supra-LT workloads. In this regard, it is advisable to perform a CPET to measure the VO2 (mL/min) and to use a lower extremity ergometer to quantify the workloads (Watts) for proper measurement of VO2/workload slope.
