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Peter Ibbott, Nick Ball, Marijke Welvaert and Kevin G. Thompson

linear encoder is considered a valid and reliable tool for measuring mean mechanical power during strength training activities. 18 The mean value per set for each mechanical parameter was recorded for analysis. Surface electromyography (sEMG) data were collected and analyzed using a portable wireless

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Glyn Howatson, Raphael Brandon and Angus M. Hunter

There is a great deal of research on the responses to resistance training; however, information on the responses to strength and power training conducted by elite strength and power athletes is sparse.

Purpose:

To establish the acute and 24-h neuromuscular and kinematic responses to Olympic-style barbell strength and power exercise in elite athletes.

Methods:

Ten elite track and field athletes completed a series of 3 back-squat exercises each consisting of 4 × 5 repetitions. These were done as either strength or power sessions on separate days. Surface electromyography (sEMG), bar velocity, and knee angle were monitored throughout these exercises and maximal voluntary contraction (MVC), jump height, central activation ratio (CAR), and lactate were measured pre, post, and 24 h thereafter.

Results:

Repetition duration, impulse, and total work were greater (P < .01) during strength sessions, with mean power being greater (P < .01) after the power sessions. Lactate increased (P < .01) after strength but not power sessions. sEMG increased (P < .01) across sets for both sessions, with the strength session increasing at a faster rate (P < .01) and with greater activation (P < .01) by the end of the final set. MVC declined (P < .01) after the strength and not the power session, which remained suppressed (P < .05) 24 h later, whereas CAR and jump height remained unchanged.

Conclusion:

A greater neuromuscular and metabolic demand after the strength and not power session is evident in elite athletes, which impaired maximal-force production for up to 24 h. This is an important consideration for planning concurrent athlete training.

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Bjørn Harald Olstad, Christoph Zinner, João Rocha Vaz, Jan M.H. Cabri and Per-Ludvik Kjendlie

Purpose:

To investigate the muscle-activation patterns and coactivation with the support of kinematics in some of the world’s best breaststrokers and identify performance discriminants related to national elites at maximal effort.

Methods:

Surface electromyography was collected in 8 muscles from 4 world-class (including 2 world champions) and 4 national elite breaststroke swimmers during a 25-m breaststroke at maximal effort.

Results:

World-class spent less time during the leg recovery (P = .043), began this phase with a smaller knee angle (154.6° vs 161.8°), and had a higher median velocity of 0.18 m/s during the leg glide than national elites. Compared with national elites, world-class swimmers showed a difference in the muscle-activation patterns for all 8 muscles. In the leg-propulsion phase, there was less triceps brachii activation (1 swimmer 6% vs median 23.0% [8.8]). In the leg-glide phase, there was activation in rectus femoris and gastrocnemius during the beginning of this phase (all world-class vs only 1 national elite) and a longer activation in pectoralis major (world champions 71% [0.5] vs 50.0 [4.3]) (propulsive phase of the arms). In the leg-recovery phase, there was more activation in biceps femoris (50.0% [15.0] vs 20.0% [14.0]) and a later and quicker activation in tibialis anterior (40.0% [7.8] vs 52.0% [6.0]). In the stroke cycle, there was no coactivation in tibialis anterior and gastrocnemius for world champions.

Conclusion:

These components are important performance discriminants. They can be used to improve muscle-activation patterns and kinematics through the different breaststroke phases. Furthermore, they can be used as focus points for teaching breaststroke to beginners.

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Jeni R. McNeal, William A. Sands and Michael H. Stone

Purpose:

The aim of this study was to investigate the effects of a maximal repeated-jumps task on force production, muscle activation and kinematics, and to determine if changes in performance were dependent on gender.

Methods:

Eleven male and nine female athletes performed continuous countermovement jumps for 60 s on a force platform while muscle activation was assessed using surface electromyography. Performances were videotaped and digitized (60 Hz). Data were averaged across three jumps in 10-s intervals from the initial jump to the final 10 s of the test.

Results:

No interaction between time and gender was evident for any variable; therefore, all results represent data collapsed across gender. Preactivation magnitude decreased across time periods for anterior tibialis (AT, P < .001), gastrocnemius (GAS, P < .001) and biceps femoris (BF, P = .03), but not for vastus lateralis (VL, P = .16). Muscle activation during ground contact did not change across time for BF; however, VL, G, and AT showed significant reductions (all P < .001). Peak force was reduced at 40 s compared with the initial jumps, and continued to be reduced at 50 and 60 s (all P < .05). The time from peak force to takeoff was greater at 50 and 60 s compared with the initial jumps (P < .05). Both knee fexion and ankle dorsifexion were reduced across time (both P < .001), whereas no change in relative hip angle was evident (P = .10). Absolute angle of the trunk increased with time (P < .001), whereas the absolute angle of the shank decreased (P < .001).

Conclusions:

In response to the fatiguing task, subjects reduced muscle activation and force production and altered jumping technique; however, these changes were not dependent on gender.

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Nicholas Tam, Ross Tucker, Jordan Santos-Concejero, Danielle Prins and Robert P. Lamberts

VICON MX motion analysis system (Oxford Metrics Ltd, Oxford, UK), sampling at 250 Hz using a modified Helen–Hayes marker set. GRF data were collected using two 900 × 600-mm force platform (AMTI, Watertown, MA), sampling at 2000 Hz, synchronized with the motion capture system. Surface electromyography

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Michael J. Davies, Bradley Clark, Laura A. Garvican-Lewis, Marijke Welvaert, Christopher J. Gore and Kevin G. Thompson

. Clancy E , Morin EL , Merletti R . Sampling, noise-reduction and amplitude estimation issues in surface electromyography . J Electromyogr Kinesiol . 2002 ; 12 ( 1 ): 1 – 16 . doi:10.1016/S1050-6411(01)00033-5 11804807 10.1016/S1050-6411(01)00033-5 24. Matthews G , Joyner L , Gilliland

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Guillaume P. Ducrocq, Thomas J. Hureau, Olivier Meste and Grégory M. Blain

preexercise to postexercise and expressed as a percentage change from preexercise (ΔQT single , ΔQT 10 , and ΔQT 100 ). A decrease in the ratio QT 10 /QT 100 (QT 10:100 ) was used as an index of low-frequency fatigue. 33 Surface Electromyography Electrical activity of the right VL, VM, and RF was recorded by

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Josu Gomez-Ezeiza, Jordan Santos-Concejero, Jon Torres-Unda, Brian Hanley and Nicholas Tam

, synchronized collection of 3-dimensional markers trajectories using a 10-camera Vicon Bonita 10 motion capture system (Vicon, Oxford, United Kingdom), ground reaction force data (AMTI, Watertown, MA), and wireless surface electromyography (myOn 320, Myon AG, Schwazenberg, Switzerland) were recorded. The 6

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Jason D. Stone, Adam C. King, Shiho Goto, John D. Mata, Joseph Hannon, James C. Garrison, James Bothwell, Andrew R. Jagim, Margaret T. Jones and Jonathan M. Oliver

Muscle activity, as measured by surface electromyography, increased for the biceps femoris and vastus lateralis over successive repetitions. 28 The brief rest afforded within the CS condition allowed a return to baseline muscle activity such that the same phenomenon was observed within each cluster. A

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Michael E. Hales and John D. Johnson II

the lead-practitioner attaching surface electromyography (EMG) electrodes to the predetermined sites of the lower extremity. Afterward, the participant ran through the test course at a low-intensity pace for 5 minutes, minus the farmer’s carry and weighted sled pull. This accomplished 2 objectives: (1