4 research outputs found

    Influence of triceps surae electromechanical delay on movement responses in the sprint start event

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    This study examined the delay in sprint start performance related to electromechanical delay (EMD) in the triceps surae muscle and aimed to determine whether sprinters may gain an advantage in sprint start response time (SSRT). SSRT’s of nineteen sprinters were measured using an International Association of Athletics Federations approved SSRT detection system. EMD times were also obtained from the triceps surae muscle during a simple heel-lift experiment. Using Brosnan et al. (2016) response time limits, the results demonstrated that EMD produced a significant moderate correlation with SSRT (r = 0.572, P = 0.01). Initial results suggest EMD influences SSRT. However greater specificity in the EMD measurement to the sprint start action is required to determine the true effects of EMD on SSRT

    Sprint start performance: the potential influence of triceps surae electromechanical delay

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    In the sprint start, a defined sequence of distinct response delays occurs before the athlete produces a movement response. Excitation of lower limb muscles occurs prior to force production against the blocks, culminating in a movement response. The time delay between muscle excitation and movement, electromechanical delay (EMD), is considered to influence sprint start response time (SSRT). This study examined the delay in sprint start performance from EMD of the triceps surae muscle and examined whether certain sprinters gain an advantage in SSRT. Nineteen experienced sprinters performed sprint starts from blocks, with SSRT measured by an International Association of Athletics Federations (IAAF)-approved starting block system. EMD times were detected during a heel-lift experiment. Using revised SSRT limits, based on concerns over the validity of the IAAF 100 ms false start limit, EMD produced a significant moderate correlation with SSRT (r = 0.572, p = 0.011). Regression analysis determined that together, EMD and signal processing time (the delay between the auditory signal and muscle excitation) accounted for 37% of the variance in SSRT. Initial results suggest EMD is part of the response time process and that certain athletes may gain a performance advantage due to reduced EMD

    Onset detection in surface electromyographic signals across isometric explosive and ramped contractions: a comparison of computer-based methods

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    Objective. Accurate identification of surface electromyography (EMG) muscle onset is vital when examining short temporal parameters such as electromechanical delay. The visual method is considered the ‘gold standard’ in onset detection. Automatic detection methods are commonly employed to increase objectivity and reduce analysis time, but it is unclear if they are sensitive enough to accurately detect EMG onset when relating them to short-duration motor events. Approach. This study aimed to determine: (1)if automatic detection methods could be used interchangeably with visual methods in detecting EMG onsets(2)if the Teager–Kaiser energy operator(TKEO) as a conditioning step would improve the accuracy of popular EMG onset detection methods. The accuracy of three automatic onset detection methods: approximated generalized likelihood ratio (AGLR), TKEO, and threshold-based method were examined against the visual method. EMG signals from fast, explosive, and slow, ramped isometric plantarflexor contractions were evaluated using each technique. Main results. For fast, explosive contractions, the TKEO was the best-performing automatic detection method, with a low bias level(4.7 ± 5.6 ms) and excellent intraclass correlation coefficient (ICC) of 0.993, however with wide limits of agreement (LoA) (−6.2 to +15.7 ms). For slow, ramped contractions, the AGLR with TKEO conditioning was the best-performing automatic detection method with the smallest bias(11.3 ± 32.9 ms) and excellent ICC(0.983) but produced wide LoA (−53.2 to +75.8 ms). For visual detection, the inclusion of TKEO conditioning improved inter-rater and intra-rater reliability across contraction types compared with visual detection without TKEO conditioning. Significance. In conclusion, the examined automatic detection methods are not sensitive enough to be applied when relating EMG onset to a motor event of short duration. To attain the accuracy needed, visual detection is recommended. The inclusion of TKEO as a conditioning step before visual detection of EMG onsets is recommended to improve visual detection reliability

    Plantarflexor electromechanical delay: influence of contraction type and muscle-tendon unit length

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    Electromechanical delay (EMD) is an important determinant of explosive neuromuscular performance. Factors such as muscle contraction type and initial muscle-tendon unit (MTU) length influence this delay period. The aim of this study is to compare differences in EMD from plantar flexors across different contraction modes and MTU lengths. EMD of physically-active individuals (n = 14) was assessed during a series of twitch and explosive isometric plantarflexions across different MTU lengths. For involuntary and voluntary explosive conditions, EMD tended to decrease while the MTU length increased from plantarflexion to neutral/dorsiflexion. No significant differences in EMD were observed between neutral and dorsiflexion MTU lengths. These results have implications for sporting performance where the ability to rapidly produce muscular force is crucial
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