Relationships among Muscle Fibre Typology, the Force-Velocity-Power relationship, and the Force-velocity profile during the Squat Jump and Sprinting

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Minahan, Clare L

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Bellinger, Phillip M

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2020-09-21
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Background: Sport Science researchers have validated a novel methodology to determine the force-velocity profile (SFv) which can be optimized in the vertical profile to maximise an athlete’s power production. This profile represents an extension upon the well-known force-velocity-power relationship (FVPr) which is based on the 1938 Hill model. Early muscle physiology researchers identified that different skeletal muscle fiber typology (MFT) exist and have categorized these fiber types according to contractile characteristics, enzyme activities, morphological, and metabolic properties. The physiological characteristics between MFT display differences in maximum shortening velocity and time to fatigue, which results in contrasting force-velocity-power (FVP) production capabilities during exercise. Human MFT is thought to be largely determined genetically, with little influence from external stimulus (i.e., exercise training), leading to a predisposition for sporting success along a sporting domain spectrum, from sprint to endurance sports. Within elite sport, athletes are tested for jumping and sprinting performance to determine; the suitability of an athlete to a given sport, identify the needs of an athlete, the responses to training, and preparedness of athletes for elite competition. Much research has investigated the FVPr variables and the SFv during jumping and sprinting. To date however, research is yet to investigate important relationships among MFT, the FVPr, and the SFv during jumping and sprinting. As such, further experimental research is required to determine such relationships, and provide important implications for performance professionals and researchers alike. Objectives: The primary objective of the research study was to to investigate apparent relationships between MFT and the mechanical variables of the SFv and the FVPr during the squat jump and sprinting. A secondary aim was to consider how those relationships may influence exercise performance. Methodology: Nineteen developing rugby league (RL) athletes were assessed for MFT, as well as the mechanical variables derived from the force- velocity-power (FVP) profiles during the squat jump and sprinting. The FVPr and SFv mechanical variables were acquired by using the computational method for both jumping and sprinting. For jumping, the participants were required to complete a series of un-loaded and loaded barbell squat jumps, whereby the highest jump from each trial was used to determine the jumping FVPr and SFv. For sprinting, two trials of 30 m sprints were completed, whereby split times were recorded at 5 m intervals. The fastest trial from each participant was used to determine the sprinting FVPr, SFv, and mechanical application of force variables. Proton magnetic resonance spectroscopy (1H-MRS) was used to quantify carnosine concentration in the gastrocnemius muscle in order to estimate MFT. The carnosine concentration was compared to that of a control population of active, non-athlete males (n=40), whereby an individual carnosine Z-score was derived for the RL athletes. Carnosine Z-score MFT groups were formed using the known group difference technique, whereby all carnosine Z-scores above zero formed the positive carnosine MFT group (n=9), and below zero formed the negative carnosine MFT group (n=10). SPSS (v26) was used to perform t-tests and spearman’s correlations to determine significant differences and relationships between carnosine Z-score MFT groups and the mechanical variables, while Microsoft Office Excel (2016) was used to analyse group variables data (sample size, mean, and standard deviation) acquired by the t-tests, to calculate Cohen’s d effects size. Results: MFT was not found to influence the SFv during jumping or sprinting, however, MFT was found to influence the FVPr, with differences for force, velocity, and power between MFT. Moderate associations were also found between carnosine Z-score and the mechanical variables (force-velocity-power). Maximal power output (PMAX) was significantly different between carnosine Z-score MFT groups during jumping (p= 0.041, d=1.01), and was moderately associated with MFT (r=0.598**). PMAX (W/kg) was thought to be most influenced by VO (m/s) (p=0.073, d=0.88) but not FO (N/kg) during the squat jump. FO (N/kg) was not significantly different between groups (p=0.920, d=0.05) and had a negligible association with MFT (r= -0.032). During sprinting the SFv was not significantly different between groups (p=0.224, d=0.58) and was not considered to be influenced by MFT (r= -0.053). PMAX (W/kg) during sprinting was found to have a significant difference between MFT groups (p=<0.001, d=2.12), and seemed to be most influenced by FO (N/kg) (r=0.858**). FO (N/kg) was also significantly different between groups (p=0.019, d=1.19), while VO was not (p=0.216, d=0.59), and VO had a low association to PMAX (r=0.030). PMAX was found to influence RFMAX with a very high correlation (r=0.993**) and RFMAX was found to be significantly different between MFT groups (p=0.001, d=1.97). Exercise performance was most associated with PMAX in both jump height (m) (r=0.801**) and 30-m sprint time (s) (r=-0.893**), and resulted in significant and highly significant differences between groups for the squat jump (p=0.038, d=1.03) and the 30-m sprint time (s) (p=<0.001, d=2.54). Conclusion: Variation in MFT was not associated with variation in the SFv during the squat jump or sprinting, despite being associated with various mechanical variables derived from the FVPr. MFT was found to influence PMAX differently during the squat jump when compared to sprinting. This is thought to be due to the low velocity constraints of the Squat jump, compared to the high velocity motion of sprinting, which highlights the difference in force production capabilities at high velocities for type IIa/ IIx MFT (Aagaard & Andersen, 1998; Tihanyi, Apor, & Fekete, 1982). The magnitude of difference between PMAX (W/kg) in sprinting when compared to the squat jump supports this inference, and is thought (Aagaard & Andersen, 1998; Tihanyi et al., 1982) to have occurred due to the low velocity constraints during the squat jump. To confirm this finding, future studies investigating associations between MFT and the FVPr, should compare FVP mechanical variables between the squat jump and high velocity jumps, such as a counter movement jump or drop jump. Future research should also aim to determine PMAX (W/kg) thresholds as associated to carnosine Z-score to better advise practitioners in the field; during baseline testing, with exercise prescription, during athlete performance monitoring, and determining athlete suitability for elite sport. While this study has determined an association between MFT, the FVPr, and has demonstrated that MFT has likely influenced the associated exercise performance. It is possible other muscle morphology differences within these groups (pennation angle and cross-sectional area), may also contribute to performance differences found, and is a recommendation for future investigation.

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Thesis (Masters)

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Master of Medical Research (MMedRes)

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School of Medical Science

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muscle fiber typology

force-velocity-power relationship

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