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Methodological considerations and reliability of visually detecting muscle activity onset during an isometric midthigh pull / SAYYAM KATHURIA
Swansea University Author: SAYYAM KATHURIA
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Abstract
The isometric midthigh pull (IMTP) is the most commonly employed multi-joint isometric test of neuromuscular function. Performance in the IMTP is associated with several dynamic tests of neuromuscular function among weightlifters, cyclists, wrestlers, powerlifters, rugby league players, NCAA D1 trac...
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Swansea University, Wales, UK
2024
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| Institution: | Swansea University |
| Degree level: | Master of Research |
| Degree name: | MRes |
| Supervisor: | Owen, N. J., and Heffernan, S. M. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa66233 |
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| Abstract: |
The isometric midthigh pull (IMTP) is the most commonly employed multi-joint isometric test of neuromuscular function. Performance in the IMTP is associated with several dynamic tests of neuromuscular function among weightlifters, cyclists, wrestlers, powerlifters, rugby league players, NCAA D1 track and field athletes and several other disciplines at the collegiate level. The test is commonly performed on a force platform (FP), for typically quantifying maximal force producing capacity or peak force (PF) and rate of force development (RFD). In an IMTP, PF has been reported as a valid and reliable output variable. However, there is lack of agreement and evidence regarding the reliability of RFD. In contrast to PF, quantification of RFD is dependent on the identification of a start-time. The start-time refers to an instant between the quiescent phase and the start of the athlete pulling, manifested by a sudden change in the expression of the vertical component of the groundreaction force (VGRF). The lack of agreement in the calculation procedures employed to quantify RFD has contributed to a lack of clarity regarding the level of reliability reported in previous studies. More importantly, the method of identifying the start-time varies across studies, contributing to the conflicting results that exist within the scientific literature. The method of identifying a start time in an IMTP remains to be validated and standardised for subsequent calculation of RFD and any other variable dependent on a start-time, e.g., time to peak force. The expression of mechanical force, often recorded using instruments such as the FP, is preceded by a physiological phenomenon of neural and muscular excitation that can be recorded using surface electromyography (sEMG). Considering the possibility of investigating the onset time of muscle excitation and subsequent mechanical forceproduction, it was proposed that temporal sEMG analysis could be used to validate a method of determining the start-time of an IMTP performed on a FP. The onset of muscular activity in single-joint isometric tests of neuromuscular function has been investigated using sEMG, but this method has not been applied to multi-joint activities such as the IMTP. Consequently, the aim of this study was to develop a reliable and valid novel method for detecting the time of muscle onset in an IMTP, which could then be used in future studies to validate a starttime based interrogation of a recorded force-time history. The study consisted of two experimental sections which, when combined, satisfied the aim of the study. Study 1 investigated the methodological considerations in the identification of the time of muscle onset (Tmo) during an isometric midthigh pull (IMTP) using visual detection, i.e., manual visual inspection of sEMG amplitude-time history. Firstly, seven pairs of muscles were identified that are activated during the performance of an IMTP. The study then established a 2-step visual detection method, which allowed the visual inspection of these muscle’s activity during the quiescent and active phases of an IMTP. The method was thereafter used for determining the Tmo corresponding to the initiation of muscular activity during a maximal voluntary contraction (MVC) in an IMTP. Study 2 investigated the reliability of the methodology developed in Study 1. This was achieved by measuring the inter and intra-rater reliabilities of onset times, detected by two raters in the seven pairs of selected muscles across three experimental conditions; ‘ON’, ‘OFF’ and ‘WL’. The study included nine male participants with experience (> 3 years) in weightlifting exercises, especially power cleans. One participant was recruited for both the ON and OFF experimental conditions while the remaining 8 participants proficient in weightlifting were categorised under WL. ON, denotesthe test condition where sensors remained on the muscles of the participant throughout all test-retest trials. This condition was designed for the visual assessment of muscle activation patterns during IMTP test-retest trials for the same individual and its effect on reliability. In contrast OFF denotes the test condition where sensors were removed and reattached to the muscles prior to each subsequent trial. The OFF test-retest condition was designed to visually assess whether sensor placement performed by a trained individual had an effect on muscle activation patterns, in terms of the reliability. WL (weightlifters) denotes the test condition that was used to categorise the resistance and weightlifting trained participants recruited in the study. This condition aimed to evaluate reliability across a group of participants, while also exploring similarities in muscle activity among individuals and its effect on reliability. Standard deviation (SD) of differences was employed as the statistical measure for determining the variation between two independent sets of muscle onset points. Visually detecting the Tmo for 14 muscles (7 pairs) was assessed using a pre-set criteria of ≤ 5 ms, variations above which measurements were deemed unreliable. SD of differences betweenthe Tmo as determined by the same rater on two separate occasions identified all 7 pairs of muscles as reliable (differences ≤ 5 ms) in each condition. SD of differences between the Tmo determined by two raters identified 3 muscle pairs as reliable, (differences ≤ 5 ms) across the three experimental conditions. These were; gastrocnemius medialis (GS) (SD of differences; ON: 0.7 ms, OFF: 0.2 ms, WL: 0.3 ms), bicep femoris (BF) (SD of differences; ON: 2.4 ms, OFF: 3.5 ms, WL: 2.5 ms) and erector spinae longissimus (ESL) (SD of differences; ON: 2.4 ms, OFF: 2.5 ms, WL: 2.3 ms). Results of both intra and inter-rater reliability demonstrate GS as the most reliable muscle across each experimental condition, demonstrating a variation of < 1 ms. Considering the results of Study 2, GS, BF and ESL are the 3 muscle pairs recommended for future temporal investigations in the IMTP. Inspection of muscle activity via sEMG traces over the course of Study 2, revealed that GS and BF were the only two muscle pairs with negligible baseline noise prior to Tmo. Automated methods of detecting Tmo, that rely on the baseline noise can therefore be applied to GS and BF, potentially accounting for limitations associated with visual detection in future studies. This thesis has reported a reliable and novel method of detecting the Tmo during an IMTP. Furthermore, the results of this thesis can be used to validate the start-time of an IMTP, contributing towards the standardisation of IMTP research methods and improved reliability of time-dependent variables. |
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| Item Description: |
A selection of content is redacted or is partially redacted from this thesis to protect sensitive and personal information. |
| Keywords: |
Neuromuscular Physiology, Electromyography, Sports Biomechanics |
| College: |
Faculty of Science and Engineering |