A national rugby player has completed his first resistance training macrocycle. Pre- and post-tests are as follows (Pre-test is first number, post-test is second number): Bodyweight 190 lb (86.5 kg) 210 lb (95.5 kg) 1 RM bench press 295 lb (134 kg) 335 lb (152.5 kg) 1 RM squat 310 lb (141 kg) 360 lbs (163.5 kg) 40-meter sprint 5.18 sec 5.16 sec Vertical jump 20.0 in (50.7 cm) 20.0 in (50.7 cm) Which of the following is the most appropriate explanation for a lack of change in the vertical jump?