Soccer is a complex sports discipline that requires players to engage in diverse high-intensity and multidirectional activities. The optimization of strength and conditioning programs requires a comprehensive understanding of the physical attributes influencing player performance. While previous research has demonstrated the influence of knee and hip extensor muscles on the performance in sprints and other explosive movements, this study aimed to establish the relationship between plantar flexor muscle strength and high-intensity actions. Back squat (BS) and calf raise (CR) one-repetition maxima as well as linear sprint (5-, 10-, 30 m) and drop jump performance from different heights (15, 30, 45 and 60 cm) were measured in 45 elite youth players (age: 16.62 ± 1.1 years). Results showed significant negative correlations between BS strength and sprint times (r = −0.60 to −0.61), confirming the importance of lower limb extensor muscle strength in short-distance sprints. While no significant correlations were found with sprint performances, CR strength was significantly associated with drop jump test results from 45 and 60 cm drop height (r = 0.36 to 0.46). These findings demonstrate that isolated CR strength positively influences the performance in actions involving rapid stretch-shortening cycles, which suggests that current strength and conditioning programs for youth soccer players should be extended to also include exercises specifically targeting the plantar flexor muscles. While this cross-sectional study provides novel insights into the complex interplay between muscle strength and soccer-specific performance, its findings need to be corroborated in longitudinal studies directly testing the impact of plantar flexor strength training.
In contrast to the findings of Keiner, Kadlubowski, Hartmann, et al. and Mck, Hartmann, Wirth, et al. , which revealed a weak, yet significant correlation between 1-RM CR and 5 to 30 m sprint performance (r = 0.68 to 0.36), the present study did not uncover any significant associations between sprint performances and 1-RM CR. The absence of correlations between 1-RM CR and sprint performance in this study may be attributed to various contributing factors. Primarily, sprinting in soccer is a biomechanically intricate movement that engages a multitude of muscle groups, not limited to the calves. While calf strength certainly plays a role in generating power during sprinting, it represents only a partial facet of the comprehensive biomechanical processes involved. The complexities of the sport necessitate the coordinated action of various lower limb muscles, including the quadriceps, hamstrings and gluteal muscles to propel players forward and maintain balance. Indeed, Pan
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estimated that the gastrocnemius muscle contributed only 37% of the total propulsive impulse during sprinting. The static and isolated nature of the calf raise exercise used for the calf strength assessment may not adequately capture the dynamic, multi-muscle actions integral to sprinting . Furthermore, individual differences in running techniques, biomechanics and fitness levels among elite youth soccer players can contribute to the lack of a discernible correlation. It must also be acknowledged that sprinting performance can be significantly impacted by genetically predetermined factors, making them difficult to modify through physical training efforts . Finally, it is important to note that the strength and conditioning programs of soccer players typically prioritize other physical attributes, such as agility, endurance or overall lower body strength, rather than calf-specific strength.
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Sports 2024, 12, 87
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While no direct associations between calf strength and sprint performance were established, our study showed significant correlations between 1-RM CR (both in absolute terms and after normalization to body mass) and the RSIs obtained from the drop jump tests performed from higher drop heights (45, 60 cm), with correlation coefficients ranging from 0.36 to 0.46. The DJ performance from lower heights (15, 30 cm) showed no significant correlation between the 1-RM CR and the RSI (r = 0.09 to 0.16). It is worth mentioning that all correlations were observed alongside ground contact times below the fast SSC threshold of <250 ms. However, it is important to recognize that ground contact times during high-intensity actions, such as sprinting, may be even shorter . One possible reason for the unique correlation between 1-RM CR and RSIs specifically from drops of 45 and 60 cm could be attributed to the increased requirement for force production during landing from greater elevations. Since h
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