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Timothy J. Gibbons and Marie-Louise Bird

magnitude. The use of unstable surfaces and devices (ie, foam roller, foam pad, Swiss ball, etc) provides a means of challenging and progressively training abdominal muscles. These core muscles play an important stabilizing role, and lack of activation of these muscles has been reported in individuals with

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Rodrigo Cappato de Araújo, Vinícius Yan Santos Nascimento, Rafaela Joyce Barbosa Torres, Francis Trombini-Souza, David Behm and Ana Carolina Rodarti Pitangui

addition of scapular abduction, compared with a standard push-up, the serratus anterior (SA) presents greater activation. 4 , 5 , 9 Another aspect for rehabilitation is the use of unstable surfaces with exercise because it is possible to increase neuromuscular demand without implementing greater overload

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Rafaela J.B. Torres, André L.T. Pirauá, Vinícius Y.S. Nascimento, Priscila S. dos Santos, Natália B. Beltrão, Valéria M.A. de Oliveira, Ana Carolina R. Pitangui and Rodrigo C. de Araújo

The aim of this study was to evaluate the acute effect of the use of stable and unstable surfaces on electromyography (EMG) activity and coactivation of the scapular and upper-limb muscles during the push-up plus (with full protraction of the scapula). Muscle activation of anterior deltoid (AD), posterior deltoid (PD), pectoralis major, biceps brachii (BB), triceps brachii (TB), upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) levels and coactivation index were determined by surface EMG in 20 young men during push-up plus performed on a stable and unstable condition (2 unstable devices applied to hands and feet). The paired t test and Cohen d were used for statistical analysis. The results showed that during the execution of the push-up plus on the unstable surface an increased EMG activity of the scapular stabilizing muscles (SA, MT, and LT) was observed, while AD and PD muscles showed a decrease. During exercise execution on the unstable surface there was a higher index of coactivation of the scapular muscles (SA–MT and UT–LT pairs). No significant differences were observed in TB–BB and AD–PD pairs. These results suggest that the push-up-plus exercise associated with unstable surfaces produced greater EMG activity levels and coactivation index of the scapular stabilizing muscle. On the other hand, the use of an unstable surface does not promote the same effect for the shoulder muscles.

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Rodrigo Cappato de Araújo, Rodrigo de Andrade, Helga Tatiana Tucci, Jaqueline Martins and Anamaria Siriani de Oliveira

The purpose of this study was to determine if performing isometric 3-point kneeling exercises on a Swiss ball influenced the isometric force output and EMG activities of the shoulder muscles when compared with performing the same exercises on a stable base of support. Twenty healthy adults performed the isometric 3-point kneeling exercises with the hand placed either on a stable surface or on a Swiss ball. Surface EMG was recorded from the posterior deltoid, pectoralis major, biceps brachii, triceps brachii, upper trapezius, and serratus anterior muscles using surface differential electrodes. All EMG data were reported as percentages of the average root mean square (RMS) values obtained in maximum voluntary contractions for each muscle studied. The highest load value was obtained during exercise on a stable surface. A significant increase was observed in the activation of glenohumeral muscles during exercises on a Swiss ball. However, there were no differences in EMG activities of the scapulothoracic muscles. These results suggest that exercises performed on unstable surfaces may provide muscular activity levels similar to those performed on stable surfaces, without the need to apply greater external loads to the musculoskeletal system. Therefore, exercises on unstable surfaces may be useful during the process of tissue regeneration.

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Vinícius Yan Santos Nascimento, Rafaela Joyce Barbosa Torres, Natália Barros Beltrão, Priscila Soares dos Santos, André Luiz Torres Pirauá, Valéria Mayaly Alves de Oliveira, Ana Carolina Rodarti Pitangui and Rodrigo Cappato de Araújo

This study evaluated the effects of instability on the EMG activity of scapular stabilizing and upper limb muscles during exercises with axial and rotational load. Twenty male volunteers (20.9 ± 1.8 years, 174.1 ± 0.04 cm, 73.17 ± 8.77 kg) experienced in strength training participated in a crossover design. Muscle activation of anterior deltoid (AD), posterior deltoid (PD), pectoralis major (PM), biceps brachii (BB), triceps brachii (TB), upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) were determined on both conditions. Participants performed a single series of 10 repetitions of bench press and fly exercises on stable (bench) and unstable (proprioceptive disc) conditions at 60% of 1-RM. The Friedman test and post hoc Dunn’s indicated that the unstable condition showed greater EMG activity for AD (P = .001) and BB (P = .002) on the fly exercise, SA (P = .001) and LT (P = .048) on the bench press, and PM (P ≤ .002) on both exercises. These results show that using an unstable surface in exercises with rotational load provides superior EMG activity of the agonist muscles, while in exercise with axial load, the instability favors EMG activity of the scapular stabilizing muscles.

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Bryan L. Riemann, Kelsey Piersol and George J. Davies

Context: Single leg balance testing is a commonly used tool in sports medicine; however, there has been no consensus on trial duration needed to obtain reliable measures. Objective: This investigation sought to determine the minimum trial duration required to obtain the highest intrasession single and average trial reliability for single leg balance testing on stable and unstable surfaces using dominant and nondominant limbs. Design: Intrasession reliability.Setting:Biomechanics laboratory. Participants: 70 healthy (35 men, 35 women), physically active young adults aged 22.8 ± 2.8 y divided into 3 subgroups (n = 10, 30, 30) across a 3-phase study. Methods:3 phases of single leg balance testing were performed. For phase 1, the duration of time each participant could maintain posture on each limb/surface were computed. Phase 2 considered performance for 6 cumulative time intervals (5s, 10s, 15s, 20s, 25s, 30s). Phase 3 served to solidify results of phase 2 by computing reliability of 15s trials. Main outcome measures: Overall stability index of the center of pressure and platform tilt. Results: Intraclass correlation coefficients for phase 2 ranged from .74 (5s interval for nondominant limb on unstable surface) to .94 (20s interval for nondominant limb on stable surface). Phase 3 intraclass correlation coefficients ranged from .66 to .78 for single trial and .85 to .92 for 3 trial average with coefficients of variation ranging from 23.9% to 40.4% for single trial and 13.8% to 23.0% for 3 trial average. Conclusions:These results ultimately suggest 15s as the optimal trial duration to provide reliable measures while reducing compensatory event occurrence.

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Andrea Biscarini, Samuele Contemori and Giuditta Grolla

Exercises executed on unstable surfaces (such as air-pressurized balls, Bosu balls, wobble boards, inflatable discs, and low-density foam platforms) are frequently employed in fitness and athletic training programs and in injury prevention and rehabilitation interventions. 1 – 7 Unstable surfaces

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Phakkanut Mathurapongsakul and Akkradate Siriphorn

administering the test on an unstable surface may improve the accuracy of the test for identifying fall risk. This study was designed to compare the accuracy of the FSST on a foam surface (FSST + foam) and the FSST for discriminating between faller older adults, nonfaller older adults, and adults. According to

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James W. Youdas, Hannah E. Baartman, Brian J. Gahlon, Tyler J. Kohnen, Robert J. Sparling and John H. Hollman

muscle recruitment in the upper erector spinae was equivalent across all 4 conditions. With these data, we refute our research hypothesis. The dual-instability condition, in which both hands and feet were fixated on unstable surfaces, did not generate greater recruitment of prime movers and torso

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Damla Karabay, Yusuf Emük and Derya Özer Kaya

surfaces. Seven CKC exercises had UT/SA ratios >1, and 4 of them were pushing exercises performed on unstable surfaces. Besides, most of the pushing exercises performed on unstable surfaces (33 of 37 exercises) had optimal ratios. Therefore, if the aim is higher activation of the SA rather than the UT