Excitation distribution of the trapezius changes in response to increasing contraction intensity, but not repeated contractions.

Upper trapezius (UT) excitation redistributes with experimentally-induced muscle pain, fatigue, and repeated contractions. Excitation distribution variability is proposed to reduce the likelihood of shoulder pain and pathology by reducing cumulative stress on musculoskeletal structures. While the middle (MT) and lower (LT) trapezius are pivotal in scapular stabilization, it remains unclear whether they display similar excitation distribution variability with repeated or increasing contraction intensity. We determined if excitation distribution of the UT, MT, and LT differ: 1) during isometric contractions at different intensities (30 % and 60 % of maximum voluntary isometric contraction (MVIC)); and 2) with repeated contractions at 60 % MVIC. Nineteen individuals completed MVICs and submaximal contractions for the UT, MT, and LT while high-density electromyography was collected. Statistical parametric mapping t-tests were performed between intensities and the 1st and 5th repetition at 60 % MVIC. UT, MT, and LT excitation distribution changed with increasing contraction intensity in 358 (∼92 % of the map), 54 (∼14 %), and 270 pixels (∼70 %), respectively. No pixels exceeded significance with repeated contractions for any muscle. Barycentre analyses revealed no significant results. These results suggest that regions of the trapezius muscle use different neuromuscular strategies in response to changes in contraction intensity and repeated contractions.

Exploring the acute muscle fatigue response in resistance trained individuals during eccentric quasi-isometric elbow flexions-a cross-sectional comparison of repetition and sex.

Eccentric quasi-isometrics (EQIs) are a novel, low-velocity resistance exercise technique that incorporates a holding isometric contraction to positional fatigue, followed by voluntary resistance of the resulting eccentric muscle action. As females are typically more fatigue resistant than males during isometric and low-velocity dynamic muscle actions, this study explored sex-differences in the muscle fatigue response to an EQI protocol. Twenty-five (n = 12 female) participants completed 4 unilateral EQI elbow flexions. Absolute and relative surface electromyography (sEMG) amplitude (iEMG, LE peak), mean power frequency (MPF), angular impulse (aIMP), and elbow angle were compared across repetitions and between sexes using discrete values and statistical parametric/non-parametric mapping. There were significant and substantial sex and repetition differences in absolute iEMG, MPF, and aIMP, however, males and females had statistically similar absolute aIMP by repetition 4. When expressed relatively, there were no significant sex-differences. Additionally, there were significant between repetition changes in sEMG amplitude and elbow angle with an increasing number of repetitions, largely in the first-two thirds of repetition time. The current study suggests that there are absolute, but not relative sex-differences in EQI induced muscle fatigue, and the effects across repetitions occur predominately in the first two-thirds of repetition time.

Ankle bracing's effects during a modified agility task: analysis of sEMG, impulse, and time to complete using a crossover, repeated measures design.

This study explored the effects of no braces, softshell (AE), and semi-rigid (T1) ankle braces on time to complete a modified agility task, as well as lower extremity muscle activity and impulse during the change of direction component of the task. Thirty-nine healthy, active individuals completed a modified agility task under the three brace conditions. Time to complete the modified agility task, along with mean surface electromyographic activity (sEMG) and impulse during the deceleration and propulsive phases of the task were measured. There were no significant differences across conditions with respect to sEMG or impulse measures during the deceleration or propulsive phases. There was a significant change in time to complete the modified agility task, F(2,76) = 17.242, p< 0.001, ηp2 = 0.312. Post-hoc analysis revealed a significant increase in time to complete the modified agility task when wearing the AE (0.16 (95% CI, 0.062 to 0.265) seconds, p< 0.001) and T1 (0.20 (95% CI, 0.113 to 0.286) seconds, p< 0.001) ankle braces compared to no braces. It appears that performance on a modified agility task may be diminished when wearing ankle braces, although sEMG activity and impulse are unaffected.

Acute effect of inhibitory kinesio-tape of the upper trapezius on lower trapezius muscle excitation in healthy shoulders.

INTRODUCTION: Shoulder pain increases excitation of the upper trapezius (UT) and reduces excitation in the lower trapezius (LT). Despite inconclusive evidence, kinesio-tape (KT) is often used to modify muscular excitation within the UT and/or LT to help correct alterations in scapular position and motion associated with shoulder pain/injury. The objective of the current study was to determine if inhibitory KT to the UT acutely increases LT excitation and if load alters the magnitude of change in the excitation observed. METHODS: Twenty-two (N = 22, 11 female) individuals with healthy shoulders (24 ± 3 years) completed 10 repetitions of an arm elevation task during 3 taping conditions (no-tape, experimental KT, sham KT) and 2 loading conditions (no load and loaded). Whole-muscle (mean grid) and spatial distribution (grid row) of LT excitation (root mean squared; RMS) was measured using a single high-density surface electromyography 32-electrode grid. RESULTS: There was a main effect for loading condition on whole-muscle LT RMS, F (1, 19) = 38.038, p < .001, partial η2 = 0.667. Whole-muscle LT RMS was significantly higher in the loaded condition (0.055 V ±0 .005) compared to the no-load condition (0.038 V ±0 .004). No effect of tape condition was observed on whole-muscle or spatial distribution of RMS. CONCLUSION: Our findings suggest that inhibitory KT to the UT does not alter whole-muscle excitation or shift the distribution of excitation within the LT during a repeated arm elevation task in healthy shoulders.

Muscle Activation in Specific Regions of the Trapezius During Modified Kendall Manual Muscle Tests.

CONTEXT: Manual muscle tests (MMTs) are often used when assessing shoulder injuries. For the trapezius, individual MMTs are used to selectively test the upper trapezius region (UTR), middle trapezius region (MTR), and lower trapezius region (LTR). The MMTs for each region are assumed to preferentially recruit the corresponding muscle fibers and produce a maximal contraction; however, whether this is true is unknown. OBJECTIVE: To determine if maximal voluntary isometric contractions (MVICs) for the upper trapezius (UT-MVIC), middle trapezius (MT-MVIC), and lower trapezius (LT-MVIC), adapted from the Kendall MMTs, recruited the corresponding trapezius regions. DESIGN: Crossover study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of young, healthy individuals (10 men, 9 women, 1 not listed; age = 23.9 ± 1.7 years, height = 171.4 ± 9.6 cm, mass = 75.7 ± 11.6 kg). INTERVENTION(S): Participants performed 3 repetitions of each MVIC. High-density surface electromyography measurements were collected from the UTR, MTR, and LTR. MAIN OUTCOME MEASURE(S): Root mean square (excitation) of the UTR, MTR, and LTR. RESULTS: We observed an increase in UTR excitation during the LT-MVIC compared with the UT-MVIC (P = .016) and MT-MVIC (P < .001). The MTR excitation increased during the MT-MVIC (P = .001) and the LT-MVIC (P < .001) compared with the UT-MVIC. We also noted an increase in MTR excitation during the LT-MVIC compared with the MT-MVIC (P < .001). The LTR excitation increased during the MT-MVIC and LT-MVIC (P values < .001) compared with the UT-MVIC. CONCLUSIONS: The UT-MVIC and MT-MVIC did not necessarily recruit the corresponding trapezius regions more than the other MVICs did. Rather, the LT-MVIC appeared to produce the greatest excitation of all trapezius regions. Additional research is needed; however, clinicians should be aware that maximal contractions may not always recruit the desired muscle region.

Ankle bracing's effects on lower extremity iEMG activity, force production, and jump height during a Vertical Jump Test: An exploratory study.

OBJECTIVE: To determine if softshell (AE) and semi-rigid (T1) ankle braces affect lower extremity iEMG activity, force, and jump height during a Vertical Jump Test. DESIGN: Repeated measures, crossover. SETTING: Laboratory. PARTICIPANTS: 42 healthy, active individuals. OUTCOME MEASURES: Vertical jump height, iEMG activity, peak vGRF. RESULTS: There was significant change across conditions in lateral gastrocnemius (LG) iEMG activity, F(2,70) = 5.31, p = .007, ηp2 = 0.132, with T1 LG iEMG being significantly less (-2.08(99% CI, -3.98 to 0.18) %MVIC, p = .004) than no brace. Significant changes were seen in rectus femoris (RF) iEMG activity, F(2,68) = 6.36, p = .003, ηp2 = 0.158, with T1 RF iEMG activity being significantly less than AE RF iEMG activity (-2.78(99% CI, -5.36 to -0.19) %MVIC, p = .005). There was a significant change in vertical jump height across conditions, F(2,78) = 22.13, p < .0005, ηp2 = 0.362, with a significant decrease in the AE (-2.41(99% CI, -3.66 to -1.17) cm, p < .0005) and T1 conditions (-2.89(99% CI,-4.56 to -1.23) cm, p < .0005), compared to no brace. CONCLUSION: Vertical jump height is significantly reduced when wearing ankle braces. Effects on lower extremity iEMG activity are dependent upon brace type.

The Effects of Ankle Braces on Lower Extremity Electromyography and Performance During Vertical Jumping: A Pilot Study.

Ankle braces have been hypothesized to prevent ankle injuries by restricting range of motion (ROM) and improving proprioception at the ankle. As such, ankle braces are commonly worn by physically active individuals to prevent ankle injuries. Despite their widespread use, the effects that ankle braces have on athletic performance measures, such as vertical jumping, remains unclear. Furthermore, although ankle braces are known to restrict normal ROM at the ankle, little is known about the effects that ankle braces have on the lower extremity proximal to the ankle, specifically muscular activation. Therefore, the purpose of this pilot study was to determine if lower extremity surface electromyographic activity (sEMG) and performance was affected in 5 males and 5 females by wearing softshell (AE) and semi-rigid (T1) ankle braces during a Vertical Jump Test, and to establish a basis for future investigation. Vertical jump height was not significantly affected (p > .05) in the AE (37.49 ± 11.61 cm) and T1 (36.3 ± 11.77 cm) ankle brace conditions, relative to the no brace (38.17 ± 12.01 cm) condition. No significant differences in sEMG of the lateral gastrocnemius and biceps femoris were present across conditions. There was a tendency for sEMG of the rectus femoris to decrease when wearing AE (195.71 ± 100.43 %MVC) and T1 (183.308 ± 92.73 %MVC) braces, compared to no braces (210.08 ± 127.46 %MVC), and warrants further investigation using a larger sample. Until more research is conducted, however, clinicians should not be concerned about ankle braces significantly affecting proximal muscle activation during vertical jumping.