Effects of Contrast Potentiation on Endurance Performance and Cardiovascular Parameters in Elite Female Soccer Players

Background/Objectives: The aim of this study was to investigate the acute effect of isometric and plyometric combined activation prior to the endurance performance assessed with the 30-15 Intermittent Fitness Test (30-15 IFT) and cardiovascular parameters. Methods: In this crossover study the data of 14 elite female soccer players aged 22.1 ± 2.9 years were assessed. The conditioning activity (CA) consisted of three sets of five seconds of maximal mid-thigh pull (IMPT), and peak force was measured, and four countermovement jumps were performed. Contact time, jump height, and reactive strength index (RSI) were assessed. Ninety seconds of rest between the sets was performed. Then, 7 min after the CA, the 30-15 IFT was performed. Results: One-way repeated measures (RM) ANOVA showed that performance during the CA did not decrease; what is more, it improved in RSI (p < 0.01). Further, paired samples t-test showed that the performance in the IFT did not change, whereas training impulse (TRIMP) was increased after CA (p = 0.039, ES = 0.61), thus the Bayesian paired test yielded only anecdotal evidence in favor of the alternative hypothesis (BF10 = 1.92; error = 2%). Conclusions: The improvement in CA suggests potentiation rather than fatigue. However, the unchanged performance alongside a modest TRIMP increase should be interpreted with caution, as TRIMP alone provides a limited assessment of physiological cost. Therefore, while the applied protocol did not enhance endurance performance, further research using multiple physiological markers is needed to clarify its impact on internal load and overall efficacy.