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Priyanka Banerjee, Stephen H.M Brown, Samuel J. Howarth and Stuart M. McGill

The ProFitter 3-D Cross Trainer is a labile surface device used in the clinic and claimed to train spine stability. The purpose of this study was to quantify the spine mechanics (compression and shear forces and stability), together with muscle activation mechanics (surface electromyography) of the torso and hip, during three ProFitter exercises. Trunk muscle activity was relatively low while exercising on the device (<25%MVC). Gluteus medius activity was phasic with the horizontal sliding position, especially for an experienced participant. Sufficient spinal stability was achieved in all three exercise conditions. Peak spinal compression values were below 3400 N (maximum 3188 N) and peak shear values were correspondingly low (under 500 N). The exercises challenge whole-body dynamic balance while producing very conservative spine loads. The motion simultaneously integrates hip and torso muscles in a way that appears to ensure stabilizing motor patterns in the spine. This information will assist with clinical decision making about the utility of the device and exercise technique in rehabilitation and training programs.

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Joanne N. Hodder, Tova E. Plashkes, Regan A. Franklin, Heather K. Hickey and Monica R. Maly

Coactivation of the knee extensors and flexors increases knee joint contact forces, which may lead to degradation of the articular surfaces. This study investigated the effect of neuromuscular fatigue induced by submaximal, repetitive, dynamic contractions on coactivation of knee musculature in young and middle-aged women. Data from 10 young women (24.6 ± 1.8 years) and 8 middle-aged women (55.4 ± 4.2 years) were analyzed. Measures included peak knee extension and flexion torques and the average amplitude of surface electromyography of rectus femoris and biceps femoris. Coactivation ratios were calculated from these activations. To induce fatigue, participants completed up to ten sets of 50 concentric knee extension and flexion contractions at 60°/s. A two-factor analysis of variance was used to determine the effect of age and fatigue. The young group showed higher peak torque compared with the middle-aged group (P < .001). During flexion, biceps femoris activity increased after fatigue when both groups were considered together (P = .018). During extension, biceps femoris activity was higher in the middle-aged than young group (P = .043). Middle-aged women exhibited a trend for greater coactivation during knee extension compared with young women (P = .066). This coactivation likely contributed to extension torque decrements in middle-aged women.

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Jennifer Di Domizio, Jeremy P.M. Mogk and Peter J. Keir

Wrist splints are commonly prescribed to limit wrist motion and provide support at night and during inactive periods but are often used in the workplace. In theory, splinting the wrist should reduce wrist extensor muscle activity by stabilizing the joint and reducing the need for co-contraction to maintain posture. Ten healthy volunteers underwent a series of 24 10-s gripping trials with surface electromyography on 6 forearm muscles. Trials were randomized between splinted and nonsplinted conditions with three wrist postures (30° flexion, neutral, and 30° extension) and four grip efforts. Custom-made Plexiglas splints were taped to the dorsum of the hand and wrist. It was found that when simply holding the dynamometer, use of a splint led to a small (<1% MVE) but significant reduction in activity for all flexor muscles and extensor carpi radialis (all activity <4% maximum). At maximal grip, extensor muscle activity was significantly increased with the splints by 7.9–23.9% MVE. These data indicate that splinting at low-to-moderate grip forces may act to support the wrist against external loading, but appears counterproductive when exerting maximal forces. Wrist bracing should be limited to periods of no to light activity and avoided during tasks that require heavy efforts.

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Sofia I. Lampropoulou and Alexander V. Nowicky

The purported ergogenic actions of transcranial direct current stimulation (tDCS) applied to motor cortex (M1) on force production and perception of effort were investigated using a 10-item numerical rating scale (0–10 NRS) in nonfatiguing bouts of a force-matching task utilizing isometric elbow flexion. Using a crossover design, 12 healthy volunteers received sham, anodal, and cathodal tDCS randomly for 10 min (1.5 mA, 62 μA/cm2) to the left M1 in a double-blind manner. Corticospinal excitability changes were also monitored using transcranial magnetic stimulation (TMS) with surface electromyography (sEMG) to monitor both motor evoked potentials (MEPs) and force-EMG from right m. biceps brachii and m. brachioradialis brachii. No significant differences between the verum and sham stimulation were obtained for elbow flexion maximum voluntary force, perception of effort, or sEMG. There were also no significant differences in MEP changes for the types of tDCS, which is consistent with reports that tDCS excitability effects are diminished during ongoing cognitive and motor activities.

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Jennifer E. Earl

Context:

Gluteus medius (GM) contraction during single-leg stance prevents the contralateral pelvis from “dropping,” providing stability for lower extremity motion.

Objective:

To determine which combination of hip rotation and abduction exercise results in the greatest activity of the GM and whether the GM responds to increased loads in these exercises.

Design and Setting:

Repeated measures, laboratory.

Subjects:

20 healthy volunteers.

Interventions:

Resistance (2.26 and 4.53 kg) was provided to 3 variations of a single-leg-stance exercise: hip abduction only, abduction-internal rotation (ABD-IR), and abduction-external rotation.

Measurements:

Muscle activity was recorded from the anterior and middle portions of the GM using surface electromyography.

Results:

ABD-IR produced the most activity in the anterior and middle sections of the GM muscle. The 4.53-kg load produced significantly more activity than the 2.26-kg load (P < .05).

Conclusions:

The GM is most active when performing abduction and internal rotation of the hip. This information could be used to develop GM-strengthening exercises.

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In-cheol Jeon, Oh-yun Kwon, Jong-hyuck Weon, Ui-jae Hwang and Sung-hoon Jung

Context:

Prone hip extension has been recommended for strengthening the back and hip muscles. Previous studies have investigated prone hip extension conducted with subjects on the floor in the prone position. However, no study has compared 3 different table hip-extension (THE) positions in terms of the activities of the back- and hip-joint muscles with lumbopelvic motion.

Objective:

To identify more effective exercises for strengthening the gluteus maximus (GM) by comparing 3 different exercises (THE alone, THE with the abdominal drawing-in maneuver [THEA], and THEA with chair support under the knee [THEAC]) based on electromyographic muscle activity and pelvic compensation.

Design:

Repeated-measure within-subject intervention.

Setting:

University research laboratory.

Participants:

16 healthy men.

Main Outcome Measures:

Surface electromyography (EMG) was used to obtain data on the GM, erector spinae (ES), multifidus, biceps femoris (BF), and semitendinosus (ST). Pelvic compensation was monitored using an electromagnetic motion-tracking device. Exertion during each exercise was recorded. Any significant difference in electromyographic muscle activity and pelvic motion among the 3 conditions (THE vs THEA vs THEAC) was assessed using a 1-way repeated-measures analysis of variance (ANOVA) with Bonferroni post hoc test.

Results:

The muscle activities recorded by EMG differed significantly among the 3 exercises (P < .01). GM activity was increased significantly during THEAC (P < .01). There was a significant difference in lumbopelvic kinematics in terms of anterior tilting (F = 19.49, P < .01) and rotation (F= 27.38, P < .01) among the 3 exercises.

Conclusions:

The THEAC exercise was the most effective for strengthening the GM without overactivity of the ES, BF, and ST muscles and lumbopelvic compensation compared with THE and THEA.

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Catriona O’Dwyer, David Sainsbury and Kieran O’Sullivan

Context:

Functional subdivisions are proposed to exist in the gluteus medius (GM) muscle. Dysfunction of the GM, in particular its functional subdivisions, is commonly implicated in lower limb pathologies. However, there is a lack of empirical evidence examining the role of the subdivisions of the GM.

Objectives:

To compare the activation of the functional subdivisions of the GM (anterior, middle, and posterior) during isometric hip contractions.

Design:

Single-session, repeated-measures observational study.

Setting:

University research laboratory.

Participants:

Convenience sample of 15 healthy, pain-free subjects.

Intervention:

Subjects performed 3 maximal voluntary isometric contractions for hip abduction and internal and external rotation on an isokinetic dynamometer with simultaneous recording of surface electromyography (sEMG) activity of the GM subdivisions.

Main Outcome Measures:

sEMG muscle activity for each functional subdivision of the GM during each hip movement was analyzed using a 1-way repeated-measures ANOVA (post hoc Bonferroni).

Results:

The response of GM subdivisions during the 3 different isometric contractions was significantly different (interaction effect; P = .003). The anterior GM displayed significantly higher activation across all 3 isometric contractions than the middle and posterior subdivisions (main effect; both P < .001). The middle GM also demonstrated significantly higher activation than the posterior GM across all 3 isometric contractions (main effect; P = .027). There was also significantly higher activation of all 3 subdivisions during both abduction and internal rotation than during external rotation (main effect; both P < .001).

Conclusions:

The existence of functional subdivisions in the GM appears to be supported by the findings. Muscle activation was not homogeneous throughout the entire muscle. The highest GM activation was found in the anterior GM subdivision and during abduction and internal rotation. Future studies should examine the role of GM functional subdivisions in subjects with lower limb pathologies.

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Benjamin Henry, Todd McLoda, Carrie L. Docherty and John Schrader

Context:

Peroneal reaction to sudden inversion has been determined to be too slow to overcome the joint motion. A focused plyometric training program may decrease the muscle's reaction time.

Objective:

To determine the effect of a 6-wk plyometric training program on peroneus longus reaction time.

Design:

Repeated measures.

Setting:

University research laboratory.

Participants:

48 healthy volunteers (age 20.0 ± 1.2 y, height 176.1 ± 16.9 cm, weight 74.5 ± 27.9 kg) from a large Midwestern university. Subjects were randomly assigned to either a training group or a control group.

Interventions:

Independent variables were group at 2 levels (training and no training) and time at 2 levels (pretest and posttest). The dependent variable was peroneal latency measured with surface electromyography. A custom-made trapdoor device capable of inverting the ankle to 30° was also used. Latency data were obtained from the time the trapdoor dropped until the peroneus longus muscle activated. Peroneal latency was measured before and after the 6-wk training period. The no-training group was instructed to maintain current activities. The training group performed a 6-wk plyometric protocol 3 times weekly. Data were examined with a repeated-measures ANOVA with 1 within-subject factor (time at 2 levels) and 1 between-subjects factor (group at 2 levels). A priori alpha level was set at P < .05.

Main Outcome Measures:

Pretest and posttest latency measurements (ms) were recorded for the peroneus longus muscle.

Results:

The study found no significant group-by-time interaction (F 1,46 = 0.03, P = .87). In addition, there was no difference between the pretest and posttest values (pretest = 61.76 ± 14.81 ms, posttest = 59.24 ± 12.28 ms; P = .18) and no difference between the training and no-training groups (training group = 59.10 ± 12.18 ms, no-training group = 61.79 ± 15.18 ms; P = .43).

Conclusions:

Although latency measurements were consistent with previous studies, the plyometric training program did not cause significant change in the peroneus longus reaction time.

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Kieran O’Sullivan, Ellen Herbert, David Sainsbury, Karen McCreesh and Amanda Clifford

Context:

The gluteus medius (Gmed) is proposed to consist of 3 functional subdivisions (anterior, middle, and posterior). Gmed weakness and dysfunction have been implicated in numerous lower extremity disorders, including patellofemoral pain syndrome (PFPS). PFPS is a knee condition that frequently occurs in females and is associated with activities such as squatting and stair climbing. There is a lack of evidence for the role of the subdivisions of the Gmed in females with and without PFPS.

Objective:

To compare muscle activation in the 3 Gmed subdivisions during 4 weight-bearing exercises in women with and without PFPS.

Design:

Single-session, repeated-measures observational study.

Setting:

University research laboratory.

Participants:

Convenience sample of 12 women with PFPS and 12 age- and gender-matched asymptomatic controls.

Intervention:

Participants performed 4 weight-bearing exercises (wall press, pelvic drop, step-up-and-over, and unilateral squat) 3 times while surface electromyography (sEMG) activity of the Gmed segments was recorded.

Main Outcome Measures:

sEMG muscle activity for each functional subdivision of the Gmed during each weight-bearing exercise was analyzed using a mixed between–within-subjects ANOVA (post hoc Bonferroni).

Results:

No statistically significant differences in muscle activation were found between the PFPS and healthy participants (P = .97). Furthermore, there were no statistically significant differences between the exercises (P = .19) or muscle fibers (P = .36) independent of group analyzed. However, the activation of the subdivisions varied according to the exercise performed (P = .003).

Conclusions:

Similar levels of muscle activation were recorded in the Gmed subdivisions of the PFPS and healthy participants during the different exercises. This is the first study to examine all 3 Gmed subdivisions in PFPS. Future studies using larger sample sizes should also investigate onset and duration of muscle activation in all Gmed subdivisions in both healthy individuals and those with PFPS.

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Paul Comfort, Amy Regan, Lee Herrington, Chris Thomas, John McMahon and Paul Jones

Context:

Regular performance (~2×/wk) of Nordic curls has been shown to increase hamstring strength and reduce the risk of hamstring strain injury, although no consensus on ankle position has been provided.

Objective:

To compare the effects of performing Nordic curls, with the ankle in a dorsiflexed (DF) or plantar-flexed (PF) position, on muscle activity of the biceps femoris (BF) and medial gastrocnemius (MG).

Participants:

15 male college athletes (age 22.6 ± 2.1 y, height 1.78 ± 0.06 m, body mass 88.75 ± 8.95 kg).

Design:

A repeated-measures design was used, with participants performing 2 sets of 3 repetitions of both variations of Nordic curls, while muscle activity was assessed via surface electromyography (EMG) of the BF and MG. Comparisons of muscle activity were made by examining the normalized EMG data as the percentage of their maximum voluntary isometric contraction.

Results:

Paired-samples t test revealed no significant difference in normalized muscle activity of the BF (124.5% ± 6.2% vs 128.1 ± 5.0%, P > .05, Cohen d = 0.64, power = .996) or MG (82.1% ± 3.9% vs 83.5 ± 4.8%, P > .05, Cohen d = 0.32, power = .947) during the Nordic curls in a PF or DF position, respectively.

Conclusion:

Ankle position does not influence muscle activity during the Nordic curl; however, performance of Nordic curls with the ankle in a DF position may be preferential, as this replicates the ankle position during terminal leg swing during running, which tends to be the point at which hamstring strains have been reported.