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Plyometric training is commonly used to improve athletic performance; however, it is unclear how each component of the muscle-tendon complex (MTC) is affected by this intervention. The effects of 14 weeks of plyometric training on the passive stiffness of the gastrocnemii muscles and Achilles tendon was determined simultaneously to assess possible local adaptations of elastic properties. The passive force-length relationship of the gastrocnemii MTC and elongation of the gastrocnemii muscles were determined using ultrasonography during passive cyclic stretching in 19 subjects divided into trained ( n = 9) and control ( n = 10) groups. An upward trend in stiffness of the gastrocnemii MTC ( P = 0.09) and a significant increase in the intrinsic gastrocnemii muscle stiffness were found ( P < 0.05). In contrast, no significant change in gastrocnemii tendon stiffness, or in muscle and tendon geometry, was determined ( P > 0.05). Considering the lack of change in gastrocnemii muscle geometry, the change in the gastrocnemii muscle stiffness may be mainly due to a change in the intrinsic mechanical properties of the muscular tissues. [ABSTRACT FROM AUTHOR]

We investigated the association of the angiotensin converting enzyme gene (ACE) insertion/deletion (I/D) polymorphism, alone or in combination with the α-actinin-3 gene (ACTN3) R577X polymorphism, with jumping (vertical squat and counter-movement jump tests) and sprint ability (30 m dash) in non-athletic, healthy young adults [N = 281 (214 male), mean (SD) age 21 (2) years]. We did not observe any effect of the ACE I/D polymorphism on study phenotypes. We repeated the analyses separately in men and women and the results did not materially change. Likewise, the mean estimates of the study phenotypes were similar in subjects with the genotype combinations ACE II + ID and ACTN3 XX or ACE DD and ACTN3 RR + RX. We found no association between the ACE DD and ACTN3 RR + RX genotype combination and performance (≥90th of the sex-specific percentile). In summary, though the ACE I/D polymorphism is a strong candidate to modulate some exercise-related phenotypes or athletic performance status, this polymorphism, alone or in combination with the ACTN3 R577X polymorphism, does not seem to exert a major influence in the muscle 'explosive' power of young healthy adults, as assessed during multi-joint exercise tests. [ABSTRACT FROM AUTHOR]