Objectives: The purpose of this study was to identify the relationship between isometric force production symmetry and jumping performance in weighted and un-weighted static and countermovement jumps (SJ and CMJ). Design: Bivariate correlation between isometric force production symmetry and vertical jump performance variables. Methods: Collegiate athletes were evaluated for this study (n=36). Subjects performed SJ, CMJ, and isometric mid-thigh pulls (IMTP). Jumps were analyzed for jump height (JH) and peak power (PP). IMTP was analyzed for peak force (PF) for left and right sides, and values were calculated to produce a peak force symmetry index (PF-SI) score. Correlational statistics were performed examining the relationship between PF-SI and jump variables. Results: Moderate statistically significant negative correlations were observed between PF-SI and all jump variables, indicating that as asymmetry increases jump performance decreases. SJ correlations weakened in weighted conditions (JH r=-0.52 @ 0 kg/r=-0.39 @ 20 kg, PP r=-0.43 @ 0 kg/r=-0.34 @ 20 kg), but CMJ produced similar correlations for both conditions (JH r=-0.47 @ 0 kg/r=-0.49 @ 20 kg, PP r=-0.28 @ 0 kg/r=-0.34 @ 20 kg). Unlike the SJ, which only contains the propulsive or concentric portion of the jump, the CMJ also contains the eccentric portion and performance contributions of the stretch-shortening cycle (SSC). The addition of the SSC may play a role in the maintaining the magnitude of asymmetry in the CMJ weighted condition. Conclusions: The results indicate that force production asymmetry may be detrimental to bilateral vertical jumping performance. The findings should be considered for further investigation on sport-specific tasks.

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The specific internal environment in the body during exercise can influence the muscle hypertrophy and strength response. Unlike chronic hypoxic exposure, exercise training under intermittent hypoxia may lead to muscle hypertrophy with relatively low workloads. Objectives: The purpose of this brief review is to discuss how a hypoxic condition can be attained without providing ambient inspiratory hypoxic gases or inducing hypobaric hypoxia. Design and Methods: Evidence-based implications and future challenges. Results: Pulse oximetry is a simple method that measures percutaneous oxygen saturation (SpO2). Several studies reported that hypoxia is produced with increasing duration of apnea, especially in the last half of the breath-hold, with SpO2 reaching levels as low as 80%. Similarly, studies have reported changes in SpO2 during dynamic exercise at various workloads with controlled frequency breathing. Conclusions and future challenges: These results suggest a possibility that moderate- or high-intensity exercise combined with controlled frequency breathing may produce a low level of SpO2, which may be a model for muscle hypertrophy by moderate- or high-intensity exercise training with hypoxia. However, there are no published studies on the effects of resistance exercise with controlled frequency breathing on muscle size and function. Additionally, it is unclear the magnitude change in SpO2 during resistance exercise with a combination of different frequencies of breathing and various workloads. Furthermore, the safety of such a technique, particularly with respect to hypercapnia and the possible elevation of arterial pressures, is also unknown and should be investigated further.

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