Reproducibility of scapular muscle activity in isokinetic shoulder flexion and extension

et al. 2019

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Background Recent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass affects the muscular activity of the shoulder stabilizers. Aim of the study was to analyzed the neuromuscular activity of the dynamic shoulder stabilizers under four combinations of stable and unstable weight mass during three shoulder exercises. It was hypothesized that a combined condition of weight with unstable mass would elicit significantly greater activation due to the increased stabilization demand. Methods Sixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 sec.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different training conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root mean square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR: U.TA/L.TA; U.TA/SA) and contraction (CR: concentric/eccentric) ratios were analyzed (paired t-test; α=0.05; Bonferroni adjusted α=0.008) Results PWG showed significantly greater muscle activity for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p>0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles. Conclusion Higher weight generated greater muscle activation whereas an unstable weight mass behavior raised the neuromuscular activity, possibly due to increased stabilization demands. Application of an unstable weight mass may be beneficial to improve training effects in shoulder prevention and rehabilitation programs.

Section: Latissimus Dorsi (Ld)mentioning

confidence: 94%

Section: Measurement Protocolmentioning

confidence: 99%

Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass

et al. 2019

Preprint

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“…In detail, six pairs of EMG-electrodes were positioned over six main shoulder muscles as reported in Table 1. 30,34,35 and EMG-MVIC assessment using an isokinetic device reported high reliability 33 . All individuals firstly performed a 5-sec isometric contraction attempt (familiarization: sub-max.…”

Section: Measurement Protocolmentioning

confidence: 97%

Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass

et al. 2019

Preprint

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Background Recent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass affects the muscular activity of the shoulder stabilizers (ST). Aim of the study was to analyzed the neuromuscular activity of the dynamic ST under four combinations of stable and unstable weight mass during three shoulder exercises. It was hypothesized that a combined condition of weight with unstable mass would elicit significantly greater activation due to the increased stabilization demand. Methods Sixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 sec.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different training conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root mean square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR: U.TA/L.TA; U.TA/SA) and contraction (CR: concentric/eccentric) ratios were analyzed (paired t-test;Bonferroni adjusted α=0.008) Results PWG showed significantly greater activation for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p>0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles. Conclusion Higher weight generated greater muscle activation whereas an unstable weight mass behavior raised the neuromuscular activity, increasing the stabilization demands. Especially in the In/Ex rotation, an unstable weight mass increased the RMS%MVIC and SR ratio. This might improve training effects in shoulder prevention and rehabilitation programs.

“…After a 1-min rest, this was followed by (ii) frontal flexion/extension arm stretched, 90°flexion in the frontal plane (90°MVIC angle). The employed positions demonstrated optimal shoulder muscles voluntary activation during isometric contraction [30,33,35] and EMG-MVIC assessment using an isokinetic device reported high reliability [34]. All individuals initially performed a 5-s isometric contraction attempt (familiarization: sub-max.…”

Section: Measurement Protocolmentioning

confidence: 99%

“…Upper trapezius (U.TA) Supero-medial and infero-lateral to a point 2 cm lateral to one-half the distance between the C7 spinous process and the lateral tip of the acromion [33] Lower trapezius (L.TA) 1/3 between the spinous process of the seventh thoracic vertebrae and the medial border of the scapula at the intersection of the scapula spine [34] Serratus anterior (SA) Over the seventh intercostal space, just anterior to the fibers of the latissimus dorsi [34] Lateral deltoid (DE) Intersection of the midpoint between the anterior and posterior deltoid muscles and the midpoint between the acromion and deltoid tuberosity [33] Latissimus dorsi (LD) Posterior axillary fold, directly lateral to the inferior tip of the scapula [33] Pectoralis major (PE) 3.5 cm medial to the anterior axillary line [33] (P), water-filled-pipe (PW), weight-pipe (PG) and weight + water-filled-pipe (PWG). Except for the initial condition (P) all other conditions were randomly ordered.…”

Section: Musclementioning

confidence: 99%

Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass

BMC Sports Sci Med Rehabil

et al. 2020

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Background: Recent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass (UWM) affects the muscular activity of the shoulder stabilizers. Aim of the study was to assess neuromuscular activity of dynamic shoulder stabilizers under four conditions of stable and UWM during three shoulder exercises. It was hypothesized that a combined condition of weight with UWM would elicit greater activation due to the increased stabilization demand. Methods: Sixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 s.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different exercise conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root-mean-square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR: U.TA/L.TA; U.TA/SA) and contraction (CR: concentric/eccentric) ratios were analyzed (paired t-test; p ≤ 0.05; Bonferroni adjusted α = 0.008). Results: PWG showed significantly greater muscle activity for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p > 0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles. Conclusion: Higher weight generated greater muscle activation whereas an UWM raised the neuromuscular activity, increasing the stabilization demands. Especially in the In/Ex rotation, an UWM increased the RMS%MVIC and SR ratio. This might improve training effects in shoulder prevention and rehabilitation programs.