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Jack M. Burns, Jeremiah J. Peiffer, Chris R. Abbiss, Greig Watson, Angus Burnett and Paul B. Laursen

Purpose:

Manufacturers of uncoupled cycling cranks claim that their use will increase economy of motion and gross efficiency. Purportedly, this occurs by altering the muscle-recruitment patterns contributing to the resistive forces occurring during the recovery phase of the pedal stroke. Uncoupled cranks use an independent-clutch design by which each leg cycles independently of the other (ie, the cranks are not fixed together). However, research examining the efficacy of training with uncoupled cranks is equivocal. The purpose of this study was to determine the effect of short-term training with uncoupled cranks on the performance-related variables economy of motion, gross efficiency, maximal oxygen uptake (VO2max), and muscle-activation patterns.

Methods:

Sixteen trained cyclists were matched-paired into either an uncoupled-crank or a normal-crank training group. Both groups performed 5 wk of training on their assigned cranks. Before and after training, participants completed a graded exercise test using normal cranks. Expired gases were collected to determine economy of motion, gross efficiency, and VO2max, while integrated electromyography (iEMG) was used to examine muscle-activation patterns of the vastus lateralis, biceps femoris, and gastrocnemius.

Results:

No significant changes between groups were observed for economy of motion, gross efficiency, VO2max, or iEMG in the uncoupled- or normal-crank group.

Conclusions:

Five weeks of training with uncoupled cycling cranks had no effect on economy of motion, gross efficiency, muscle recruitment, or VO2max compared with training on normal cranks.

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Mitchell L. Cordova, Lisa S. Jutte and J. Ty Hopkins

Many types of rehabilitation exercises are used to reestablish lower extremity neuromuscular function and strength following ankle injuries. It has not been established which exercise induces the greatest leg muscle activity, which might allow patients to recover more quickly from their injuries. The purpose of this investigation was to establish which exercises induce the most muscle activity in the medial gastrocnemius (MG), peroneus longus (PL), and tibialis anterior (TA), as measured by integrated electromyography (I-EMG). Participants (N = 24, age = 22 ± .59, mass = 63.5 ± 2.1 kg, ht = 165.7 ± 1.2 cm) conducted five repetitions of each of four exercise conditions for 30 s: one-legged stance (OLS), OLS on trampoline (OLST), T-Band kicks (TBK), and OLS perturbations (OLSP). It was found that the TBK exercise induces greater I-EMG in all three muscles, the OLST exercise stimulates more I-EMG activity in the MG and TA, and the OLSP exercise induces greater I-EMG activity in the TA.

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François Billaut and Kurt Smith

The ability to repeatedly generate maximum power output is usually accompanied by neuromuscular adjustments.

Purpose:

This study aimed to explore the occurrence of arterial O2 desaturation during prolonged repeated-sprint ability (RSA) testing and its relationship to neuromuscular activity, as evidenced by changes in surface integrated electromyogram (iEMG).

Methods:

Fifteen, national-level soccer players performed twenty 5-s cycle sprints (25 s of rest). Mechanical work and surface iEMG of the vastus lateralis (VL) and rectus femoris (RF) of the dominant lower limb were recorded for every sprint. Arterial O2 saturation (S O2) was estimated via pulse oximetry and rating of perceived exertion (RPE) recorded immediately after every sprint.

Results:

Over the sprints, mechanical work (23.5%), iEMG (VL: 14.2%, RF: 16.4%) and S O2 (3.5%) decreased, and RPE progressed to 19 (all P < .05). There was a strong linear relationship (R2 = .83, P < .05) between the changes in mechanical output and iEMG during the sprints. More importantly, changes in S O2 accompanied changes in mechanical work, iEMG and RPE (R2 = .68, R2 = .64, R2 = .62, P < .05, respectively).

Conclusion:

The study suggests that in a homogenous group of athletes a progressive arterial O2 desaturation develops during a prolonged RSA test, which may contribute toward performance regulation via an effect on sense of effort and neuromuscular activity.

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Michael P. Godard, David L. Williamson, David A. Porter, Gregory A. Rowden and Scott W. Trappe

This investigation examined alterations in neuromuscular drive for dynamic and static muscle contractions, muscle strength, and cross-sectional area (CSA) with a 12-week progressive resistance-training program (PRT). Nine healthy men (70.0 ± 1.7 years) were evaluated for maximal and submaximal neuromuscular drive (integrated electromyography [IEMG]), whole-muscle strength, isokinetic power, and thigh CSA. The results demonstrated no significant differences pre- to post-PRT in the submaximal IEMG signals (p > .05). IEMG increased (p < .05) for the maximal static contraction (29% ± 12%) and isokinetic velocities concentrically and eccentrically. There was an increase (p < .05) in maximal static strength (27% ± 5%), isokinetic concentric and eccentric strength, muscle power, IRM (47% ± 6%), and CSA (6% ± 1%; p < .05). The results reveal significant neuromuscular-drive alterations in concentric and eccentric dynamic contractions with PRT in older men and indicate that their neuromuscular drive contributes significantly to improving their concentric and eccentric skeletal-muscle strength.

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Susan J. Hall, Jane A. Kent and Vern R. Dickinson

Prolonged trapezing during sailing often results in low back pain among elite sailors. Modifications of the trapeze harness have been proposed as one approach to ameliorating this problem. To evaluate six harnesses incorporating novel features that had tested well during pilot work, myoelectric activity was monitored at C5, T6, and L5 levels of sacrospinalis and at an abdominal site while five elite sailors wore the harnesses. Integrated EMG (IEMG) values were stored by a microcomputer at periodic intervals during each 10-min trial, as each subject maintained a static horizontal trapezing position in the laboratory. Factorial repeated-measures ANOVA indicated no change in IEMG values over time, but significant (p<0.001) differences among harnesses at all four electrode sites. Features of trapeze harness design that appear to minimize muscular tension include heavy, rigid padding throughout the harness, full-length shoulder-to-buttocks support of the trunk, and adjustable leg strap supports as opposed to a crotch strap.

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Eiji Yamada, Takashi Kusaka, Satoshi Tanaka, Satoshi Mori, Hiromichi Norimatsu and Susumu Itoh

Objective:

To investigate changes in motor-unit activity and muscle oxygenation (MO) during isometric contraction with and without vascular occlusion using surface electromyography (EMG) and near-infrared spectroscopy.

Design and Setting:

MO and EMG of the right vastus medialis muscle were measured during isometric contraction at 30%, 50%, and 70% maximal voluntary contraction (MVC), with and without vascular occlusion.

Participants:

6 healthy men.

Results:

Integrated EMG (IEMG) and mean power frequency were significantly higher with vascular occlusion at 30% and 50% MVC. MO reduction at each load was significantly lower with vascular occlusion. A significant positive correlation was found between IEMG and changes in MO level under both conditions.

Conclusions:

These results suggest that oxygen supply to active muscles was impaired by occlusion and that type II fibers were then preferentially recruited, which suggests that hypertrophy occurs in low-intensity exercise in patients with limitations resulting from advanced age, pain, or postsurgery limitation.

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Brian Caulfield, Tara Crammond, Angela O’Sullivan, Susan Reynolds and Tomas Ward

Context:

Identification of motor control deficit associated with Functional Instability (FI) of the ankle joint.

Objective:

T o compare patterns of ankle muscle activation during jump landing in participants with FI and a control group.

Design:

Cross-sectional comparison.

Setting:

Research laboratory.

Participants:

Twelve participants with FI (6 m, 6 f; age, 26.4 ± 4.6 years) and 10 control subjects (5 m, 5 f; age 24.9 ± 2.5 years).

Main Outcome Measures:

Integrated electromyographic (IEMG) activity of ankle musculature in the 150-millisecond period immediately prior to and post impact during 2 different jump landing activities.

Results:

Participants with FI demonstrated a significant reduction in pre-impact peroneus longus IEMG activity during both jumping activities compared to controls (P < .05). There were no significant differences between the groups’ soleus or tibialis anterior IEMG activity during the pre- or post-impact periods.

Conclusions:

These results help to further our understanding of changes in control of ankle movement during dynamic activity in participants with FI.

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Ossi Aura and Jukka T. Viitasalo

Four track and field athletes were subjects in a study that analyzed seven jumping exercises and flop-style high jump takeoffs for ground reaction forces, knee angular kinematics, and electromyographic activities of knee extensor musculature. The ground contact times varied between 177 ±13 (flop) and 278 ±25 ms (standing five jumps). The peak ground contact forces were from 5002±130 N (special drop jump) to 8202±901 N (ranning five hops). Average knee angular velocities were highest in the eccentric phase of the flop takeoff (ω = 7.1 ± 2.1 rad × s-1). Electromyographic activities before the ground contact and during the eccentric phase of contact were highest in the flop-style high jump, while during the concentric phase of contact a special drop jump exercise showed the highest activity. Preactivity IEMG correlated with the eccentric IEMG, force, and knee angular velocity positively and with the contact time negatively (p<0.001), while eccentric IEMG correlated with the eccentric force and angular velocity positively and with the contact time negatively (p<0.001).

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Stéphane Perrey, Guillaume Millet, Robin Candau and Jean-Denis Rouillon

The purpose of this study was to examine the effects of speed on the stretch-shortening cycle (SSC) behavior during roller ski skating. Ten highly skilled male cross-country skiers roller skied at 4.56, 5.33 m · s–1 and maximal speed using the V2-alternate technique on a flat terrain. Knee and ankle joint kinematics, and EMG of the vastus lateralis (VL) and gastrocnemius lateralis (GL) muscles were recorded during the last 40 s of each bout of roller skiing. Maximal speed was associated with increases in cycle rate combined with decreases in cycle length. For VL, no significant differences were observed for the integrated EMG eccentric-to-concentric ratio (iEMG Ecc/Conc) and for the stretching velocity over the range of speeds. For GL, stretching velocity and iEMG Ecc/Conc were significantly greater at maximal speed. The analysis of GL EMG activity suggests that speed improved GL stiffness so that more elastic energy was stored, a better force transmission occurred, and coupling time decreased. These findings suggest that the efficiency of roller ski skating locomotion may be increased with speed through a better use of the stretch-shortening cycle pattern in the ankle extensors.

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Andrew Renfree, Julia West, Mark Corbett, Clare Rhoden and Alan St Clair Gibson

Purpose:

This study examined the determinants of pacing strategy and performance during self-paced maximal exercise.

Methods:

Eight well-trained cyclists completed two 20-km time trials. Power output, rating of perceived exertion (RPE), positive and negative affect, and iEMG activity of the active musculature were recorded every 0.5 km, confidence in achieving preexercise goals was assessed every 5 km, and blood lactate and pH were measured postexercise. Differences in all parameters were assessed between fastest (FAST) and slowest (SLOW) trials performed.

Results:

Mean power output was significantly higher during the initial 90% of FAST, but not the final 10%, and blood lactate concentration was significantly higher and pH significantly lower following FAST. Mean iEMG activity was significantly higher throughout SLOW. Rating of perceived exertion was similar throughout both trials, but participants had significantly more positive affect and less negative affect throughout FAST. Participants grew less confident in their ability to achieve their goals throughout SLOW.

Conclusions:

The results suggest that affect may be the primary psychological regulator of pacing strategy and that higher levels of positivity and lower levels of negativity may have been associated with a more aggressive strategy during FAST. Although the exact mechanisms through which affect acts to influence performance are unclear, it may determine the degree of physiological disruption that can be tolerated, or be reflective of peripheral physiological status in relation to the still to be completed exercise task.