Divide class into two groups for 20-minute workouts. Allow for 2-minute transition between intervals. This self-guided workout follows each athlete's pace. Zone 1: 20-minute speed play with 500m/600m repeats and 60-second recovery. For outdoor runs: 250m/300m out and back, or a timed run of 60-75 seconds. Zone 2: 20-minute erg workout in two groups alternating between rowers and ski ergs. Groups switch machines after 10 minutes, alternating between RPE 8 and RPE 5 for calorie targets. Erg efforts maintain higher intensity due to shorter duration