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Hsiao-Yun Chang, Chen-Sheng Chen, Shun-Hwa Wei and Chi-Huang Huang

Context:

Fatigue of the shoulder rotator muscles may negatively affect joint position sense (JPS) and ultimately lead to injury.

Objective:

Recovery of shoulder JPS after muscle fatigue.

Design:

A repeated-measures study.

Setting:

Musculoskeletal research laboratory.

Patients:

Thirteen subjects participated in joint position error tests and isokinetic concentric strength assessment in shoulder rotation, before and after rotator muscle fatigue.

Interventions:

Local muscle fatigue was induced using isokinetic concentric contractions of the shoulder rotator muscles.

Main Outcome Measurements:

Shoulder rotator strength and JPS error signals were measured before fatigue, immediately after fatigue, and every ten minutes thereafter for one hour.

Results:

Before shoulder rotation muscle fatigue, the accuracy of shoulder JPS was 2.79 ± 1.67 degrees. After muscle fatigue, the accuracy decreased to 6.39 ± 2.90 degrees. Shoulder JPS was influenced up to 40 minutes after muscle fatigue, but shoulder strength was only affected for 10 minutes after muscle fatigue.

Conclusions:

Proprioceptive recovery was slower than strength following fatigue of the shoulder rotators.

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Igor Ramathur Telles Jesus, Roger Gomes Tavares Mello and Jurandir Nadal

During muscle fatigue analysis some standard indexes are calculated from the surface electromyogram (EMG) as root mean square value (RMS), mean (Fmean), and median power frequency (Fmedian). However, these parameters present limitations and principal component analysis (PCA) appears to be an adequate alternative. In this context, we propose two indexes based on PCA to enhance the quantitative muscle fatigue analysis during cyclical contractions. Signals of vastus lateralis muscle were collected during a maximal exercise test. Twenty-four subjects performed the test starting at 12.5 W power output with increments of 12.5 W⋅min–1, maintaining cadence of 50 rpm until voluntary exhaustion. The epochs of myoelectric activation were identified and used to estimate the power spectra. PCA was then applied to the power spectra of each subject. The standard (ST) and Euclidean (ED) distances were employed to estimate the alteration occurred due to fatigue. For comparison, the standard indexes were calculated. ST, ED, and RMS value were adequate for muscle fatigue analysis. Among these parameters, ST was more sensitive with higher effect size. Moreover, the Fmean and Fmedian were not sensitive to fatigue. The proposed method based on PCA of EMG in frequency domain allowed producing fatigue indexes suitable for cyclical contractions.

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Lee Herrington

Context:

A number of acute and overuse knee pathologies share a mechanism involving a poor dynamic alignment of the limb creating increased stress in the tissues. Inappropriate execution of a correct strategy during landing has been suggested to involve insufficient activity of the hip abductor and external rotator muscles. Limited data describing the relationships between hip-abductor muscle fatigue and hip/knee joint mechanics exists.

Objective:

To investigate the effect of fatigue of the hip abductor muscles on knee valgus angle.

Design:

Repeated measures.

Participants:

30 asymptomatic subjects: 15 female (age 20.4 ± 1.4, range 18–26 years; height 1.66 m, range 1.60–1.76 m; weight 63.9 kg, range 58–68 kg) and 15 male subjects (age 22 ± 3.2, range 18–28 years; height 1.84 m, range 1.65–1.90 m; weight 82.1 kg, range 69–93 kg).

Main outcome Measures:

Knee valgus (frontal plane projection) angle was assessed during a step landing task before and following a fatiguing protocol of the hip abductor muscles involving repeated 10 s maximal isometric contractions of the hip abductor muscles, until strength was recorded as 50% of preintervention score.

Results:

Males showed no significant change in knee valgus angle at initial ground contact (p = .9 ES 0.1) or in maximum knee valgus (p = .64 ES 0.5) following the fatiguing. Females showed a significant increase in maximum knee valgus angle following the fatiguing (p = .0018 ES 1.0), though the knee valgus angle at initial contact was not changed (p = .12 ES 0.67). They also demonstrated a significant increase in the change in knee valgus angle between initial contact and maximum following the fatiguing (p = .0004 ES 0.88).

Conclusion:

Females appear more susceptible to the effects of hip muscle fatigue, leading to a detrimental change in landing kinematics which may then predispose them to knee injury.

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Yukio Takihara, Yukio Urabe, Gaston Ariel Nishiwaki, Kosuke Tanaka and Koji Miyashita

Context:

Back-muscle fatigue and lumbar curvature are related to low back pain, but the relation between them is unknown.

Objective:

To clarify whether lumbar curvature changes with back-muscle fatigue.

Design:

Prospective pseudorandomized.

Setting:

Laboratory.

Participants:

13 healthy men without low back pain.

Intervention:

To induce back-muscle fatigue, subjects performed a repetitive prone back-extension exercise from 45° to 0° until exhaustion and then rested 10 min. They performed this exercise 3 times.

Main Outcome Measures:

Before the trial and after each exercise, lumbar curvature was measured with a Spinal Mouse.

Results:

After back-muscle fatigue, lumbar curvature decreased significantly (P < .01). This decrease occurred at L4–S1, which was defined as the lower spine. On the contrary, curvature of the upper lumbar spine, at Th12–L4, did not decrease.

Conclusion:

Lumbar curvature, especially the lower portion, decreased with back-muscle fatigue induced by prone back-extension exercise.

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Yann Le Mansec, Jérôme Perez, Quentin Rouault, Julie Doron and Marc Jubeau

the knee flexors, respectively). 9 Because of the high influence of technical parameters on performance in badminton, it is of critical importance to evaluate the impact of muscle fatigue on specific motor skills, which appears to be the most relevant parameters at high level. 2 , 3 In the setting

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Sebastian Klich, Bogdan Pietraszewski, Matteo Zago, Manuela Galli, Nicola Lovecchio and Adam Kawczyński

Overhead sports (eg, handball, volleyball, javelin throw or tennis) are characterized by frequent expressions of high power levels (force and velocity parameters). 1 These repetitive actions can lead to an increased risk of chronic muscle fatigue and overuse syndromes. Overloadings may result in

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Razie J. Alibazi, Afsun Nodehi Moghadam, Ann M. Cools, Enayatollah Bakhshi and Alireza Aziz Ahari

pathologies. However, other studies suggest that the changes in scapular orientation have minimal effects on the subacromial space width. 27 , 28 The effect of muscle fatigue on shoulder kinematics is well investigated in healthy nonsymptomatic individuals. However, GJH individuals with inherent

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Kazem Malmir, Gholam Reza Olyaei, Saeed Talebian, Ali Ashraf Jamshidi and Majid Ashraf Ganguie

orientation refers to the control of body alignment relative to gravity and environment. Postural stability is related to the control of the body’s center of mass with respect to the center of pressure. 2 Procedure of postural stability may be influenced by various conditions, including muscle fatigue. 3

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Hidetomo Suzuki, Kathleen A. Swanik, Kellie C. Huxel, John D. Kelly IV and C. Buz Swanik

Objective:

To determine the effect of scapular fatigue on shoulder and elbow kinematics and accuracy.

Design:

Pretest–posttest.

Setting:

Laboratory.

Participants:

30 healthy men.

Interventions:

Subjects performed seated overhead throws into a target before and after a standardized scapular-muscle-fatigue protocol.

Main Outcome Measurements:

Shoulder and elbow kinematic data were analyzed during throwing. Scapular upward rotation was measured (0°, 45°, and 90° humeral elevation in scaption) with an inclinometer. Throwing accuracy was measured as mean error distance from the target (cm).

Results:

After fatigue, there was a significant increase in total elbow motion (12 % more in cocking phase, P < .05) and elbow velocity in the follow-through phase (average and maximum into flexion, P < .05). Throwing accuracy decreased 26% after fatigue (P < .05).

Conclusions:

Scapular-muscle fatigue results in compensatory motions at the elbow that might affect performance and contribute to elbow pathologies.

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Jeanne Dekerle and James Paterson

Purpose:

To examine muscle fatigue of the shoulder internal rotators alongside swimming biomechanics during long-duration submaximal swimming sets performed in 2 different speed domains.

Methods:

Eight trained swimmers (mean ± SD 20.5 ± 0.9 y, 173 ± 10 cm, 71.3 ± 10.0 kg) raced over 3 distances (200-, 400-, 800-m races) for determination of critical speed (CS; slope of the distance–time relationship). After a familiarization with muscle isokinetic testing, they subsequently randomly performed 2 constant-speed efforts (6 × 5-min blocks, 2.5-min recovery) 5% above (T105) and 5% below CS (T95) with maximal voluntary contractions recorded between swimming blocks.

Results:

Capillary blood lactate concentration ([La]), rating of perceived exertion (RPE), peak torque, stroke length, and stroke rate were maintained throughout T95 (P < .05). [La], RPE, and stroke rate increased alongside concomitant decreases in maximal torque and stroke length during T105 (P < .05) with incapacity of the swimmers to maintain the pace for longer than ~20 min. For T105, changes in maximal torque (35.0 ± 14.9 to 25.8 ± 12.1 Nm) and stroke length (2.66 ± 0.36 to 2.23 ± 0.24 m/cycle) were significantly correlated (r = .47, P < .05).

Conclusion:

While both muscle fatigue (shoulder internal rotators) and task failure occur when swimming at a pace greater than CS, the 2.5-min recovery period during the sub-CS set possibly alleviated the development of muscle fatigue for the pace to be sustainable for 6 × 5 min at 95% of CS. A causal relationship between reduction in stroke length and loss of muscle strength should be considered very cautiously in swimming.