Author(s): BEHRENS, M., HUSMANN, F., WEIPPERT, M., FELSER, S., BIELITZKI, R., BEHRENDT, T., SCHEGA, L., BRUHN, S., GUBE, M. , Institution: UNIVERSITY OF APPLIED SCIENCES FOR SPORT AND MANAGEMENT POTSDAM, Country: GERMANY, Abstract-ID: 2075

INTRODUCTION:
The countermovement jump (CMJ) and squat jump (SJ) are two basic movements that are required during physical activities and are used to monitor human performance. CMJ height is almost always greater than SJ height and the difference is thought to reflect the efficiency of utilizing the slow stretch-shortening cycle (SSC). The mechanisms contributing to the performance enhancing effect of the SSC include history-dependent muscle properties, recoil of elastic energy, pre-activation, and stretch reflexes. Although studies have investigated the mechanisms of the jump-dependent differences in performance, hardly any data exists on the effect of repetitive maximal CMJ and SJ performed until exhaustion on motor performance fatigue of the quadriceps muscle (i.e. decline in isometric maximal voluntary torque (IMVT)) as well as its neural (i.e. voluntary activation) and muscular (i.e. contractile function) underpinnings. It was assumed that a lower number of repetitions will be achieved in the CMJ compared to the SJ condition, with unique SSC-dependent neural and muscular adjustments.
METHODS:
In a randomized, counterbalanced, crossover design, 14 males performed repetitive maximal CMJ and SJ every 4s until exhaustion, defined as a drop in jump height by 50%. Using peripheral electric nerve stimulation and dynamometry, neuromuscular function was assessed before and after exercise during each condition to analyze the impact of jump type (CMJ, SJ) on motor performance fatigue and its neural and muscular determinants. Additionally, mean heart rate (HR), blood lactate concentration (BLC), and effort perception were recorded during exercise. Motor performance fatigue as well as its neural and muscular determinants were quantified as percentage pre-post changes in IMVT (ΔIMVT), voluntary activation (ΔVA), and quadriceps twitch torque evoked by paired electrical stimuli at 100 Hz (ΔPS100), respectively.
RESULTS:
Participants tended to perform fewer repetitions during CMJ compared to SJ (CMJ: 510±164, SJ: 663±308, p=0.081), while HR (CMJ: 165±15bpm, SJ: 164±17bpm, p=0.410), BLC (CMJ: 4.1±2.3mmol/l, SJ: 3.8±3.0mmol/l, p=0.370), and effort perception (CMJ: 16.5±1.7, SJ: 16.8±1.0, p=0.455) were similar between conditions. Furthermore, no differences between conditions were found for ΔIMVT (CMJ: -29.1±17.5%, SJ: -25.7±8.5%, p=0.429), ΔVA (CMJ: -30.4±21.4%, SJ: -34.9±16.7%, p=0.380), and ΔPS100 (CMJ: -16.4±20.8%, SJ: -22.7±19.9%, p=0.296)
CONCLUSION:
Participants tended to perform a lower number of CMJ compared to SJ, while indices of internal load (HR, BLC, effort perception), motor performance fatigue, and the decrease in neuromuscular function were comparable between conditions. This might be related to the involvement of the slow SSC, which resulted in a greater jump height and mechanical strain during the CMJ, probably leading to an earlier exercise termination accompanied by the same extent of motor performance fatigue and neuromuscular impairments.