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Parkinson, A, 2024. Strength and inter-limb asymmetry: methods of assessment and longitudinal monitoring in athletes. PhD, Nottingham Trent University.
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Abstract
The measurement of strength and its associated asymmetries is widespread in both research and applied practice as a diagnostic tool for injury mitigation and training monitoring. Although isokinetic dynamometry is considered the gold-standard for the assessment of maximum strength, it is unclear if an optimal measurement approach exists which poses implications for interpretation of results. The time and financial burden associated with dynamometry also means it is generally unfeasible in an applied environment and so, field-based alternatives have been implemented to measure functional strength. The purpose of this research was to review and interrogate the methods associated with measuring strength and inter-limb asymmetry using lab- and field-based testing methods for athlete monitoring. The research findings may be useful in improving standards and data quality in research and practice by offering time- and cost-effective alternatives to elaborate strength testing associated with gold-standard practice.
A systematic review of the literature retrieved a total of 3,594 articles utilising methods to assess strength and inter-limb asymmetry, of which 53 articles met the inclusion criteria for the study. Various measurement strategies were employed to assess strength across a diverse range of populations, with the two most common methods of testing being isokinetic dynamometry (n = 25, 50%) and jumping/hopping (n = 28, 53%). The review identified 12 index types used to calculate inter-limb asymmetry; however, only four of them were unaffected by the limitations associated with selecting a reference limb, resulting in potentially inflated and variable scores. Interpretation was largely based on an arbitrary threshold of 10-15% but only two of the 18 articles which referenced the threshold cited original evidence for its utility in identifying ‘abnormal’ asymmetry. Asymmetry scores ranged between and within populations from approximate symmetry to asymmetries larger than 15% and variable effects were observed in relation to injury risk and performance, indicating an individual approach to asymmetry assessment and interpretation is likely necessary.
The second study aimed to establish the effect of the number and location of torque-angle measurements to assess isometric strength characteristics using isokinetic dynamometry. A simple quadratic function was used to derive the relationship between joint torque and angle in a monoarticular representation of the knee joint in simulated and experimental data. Protocols which measured torque at a single joint angle demonstrated gross underestimations in peak torque for measurement angles that were further away from the optimal angle, particularly for narrower torque-angle profiles. Protocols which utilised multiple measurement angles identified larger errors in prediction of torque-angle characteristics for combinations with fewer measurement angles. However, in instances where an extensive protocol is not feasible, practitioners should adopt a protocol with a spread of measurements angles throughout the joint range, as well as a joint angle near the expected optimum, to improve the accuracy of torque-angle parameter predictions.
The purpose of the third study was to assess the utility of field-based alternatives to isokinetic dynamometry for the assessment of lower limb strength and inter-limb asymmetry. Maximum voluntary isometric contractions (MVIC) of the knee flexors and extensors were assessed on the dominant and non-dominant limb for comparison with a battery of unilateral functional tests: the isometric midthigh pull (IMTP), countermovement jump (CMJ) and horizontal jump (HJ). Functional tests demonstrated acceptable absolute and relative within session reliability across the selected performance variables, but the CMJ exhibited more variability than the other two tests. Bland-Altman analyses revealed smaller systematic bias and narrower limits of agreement for the HJ compared to the other field-based tests, particularly in jump distance, which highlights it as a simple and low-cost method for assessing functional strength adaptations that can be considered meaningful and real. Although significant positive relationships were observed between knee flexor/extensor MVICs and some functional tests, predictors accounted for ≤ 30% of the variance in the outcome. Between limb differences were also inconsistent between maximum and functional tests which highlights obvious task differences and strength qualities being assessed. However, inter-limb asymmetry determined by dynamometry demonstrated significant positive relationships with both maximum and functional strength. Likewise, inter-limb asymmetry determined by functional tests was significantly and positively correlated with maximum and functional strength. This indicates the potential utility of field-based alternatives for the identification of inter-limb asymmetries in muscular strength. Lastly, larger asymmetries were generally associated with better isometric strength and functional performance which indicates asymmetries of larger magnitude may be expected from stronger athletes.
The final study aimed to monitor functional strength and inter-limb asymmetry across an athletic season using field-based methods that are easily accessible and implementable in an applied environment. Vertical and horizontal jump performance and inter-limb asymmetry were assessed in team-sport athletes (N = 38) across an athletic season, and comparisons were made between sexes (male and female) and sports (netball, basketball, and hockey). Performance-based metrics (jump height and distance) for the CMJ and HJ identified sex- and sport-specific fluctuations across the season. Inter-limb asymmetry in unilateral jump performance also identified significant reductions in HJ asymmetry which coincided with improvements in HJ distance, but no changes were observed in unilateral CMJ height or CMJ asymmetry. This reiterates the diagnostic capability of the HJ to detect meaningful changes in performance and inter-limb asymmetry as indicated initially in cross-sectional data. However, the association between asymmetry magnitude and performance relates better performance with reduced asymmetries which is inconsistent with the correlations observed in the previous study. Differences in testing methods (CMJ/HJ performance metrics vs dynamometry, IMTP, CMJ and HJ performance and kinetics) and timepoints (cross-sectional vs longitudinal) as well as participant characteristics (males from one sport vs males and females from multiple sports) may, however, partly explain the lack of clarity regarding the relationship between inter-limb asymmetry and performance. Slight to moderate levels of agreement in asymmetry direction were found in the CMJ and HJ when assessed between timepoints and tests, which confirms previous indications of directional inconsistencies in which limb is favoured across measures. Therefore, seasonal fluctuations in jumping performance can be expected amongst team-sport athletes, with variation between sexes and sports. Interpretation of asymmetry magnitude without direction is cautioned against, as meaningful differences in performance can be overlooked due to directional inconsistencies within- and between-tests. Relationships between asymmetry and performance should be considered in relation to methodological decisions and sample characteristics, due to the highly variable nature of asymmetry.
Collectively, this research has demonstrated the utility of both lab- and field-based methods for the assessment of muscular strength and inter-limb asymmetry. Measurement of isometric strength characteristics using dynamometry can be improved, even when using selective measurement protocols, which reduces the barriers to gold-standard practices in the applied environment. Functional strength tests also offer provide reliable and valid indications of maximum strength and inter-limb asymmetry; however, variability should be expected between populations and tests. The magnitude and direction of inter-limb asymmetry are highly inconsistent, and so interpretation for monitoring and training purposes should be specific to the context of investigation to ensure appropriate conclusions and decision-making.
| Item Type: | Thesis |
|---|---|
| Creators: | Parkinson, A. |
| Contributors: | Name Role NTU ID ORCID |
| Date: | July 2024 |
| Rights: | The copyright in this work is held by the author. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of the information contained within this document should be fully referenced, quoting the author, title, university, degree level and pagination. Queries or requests for any other use, or if a more substantial copy is required, should be directed to the author. |
| Divisions: | Schools > School of Science and Technology |
| Record created by: | Jeremy Silvester |
| Date Added: | 25 Apr 2025 14:57 |
| Last Modified: | 25 Apr 2025 14:57 |
| URI: | https://irep.ntu.ac.uk/id/eprint/53460 |
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