Figure 3. Evolution of heart rate (HR, expressed as a percentage of peak heart rate (HR) reached during the original 30-15) for Group A and B as a function of relative exercise intensity during the four protocols (30-15 : original 30-15, 30-15 : modified version of the 30-15 without resting periods, 30-15 : modified version of the 30-15 without changes of direction, 30-15 : modified version of the 30-15 with 28-m shuttles.) *: p < 0.05 vs. 30-15 (A), † : p < 0.05 vs. 30-15