No difference in 1RM strength and muscle activation during the barbell chest press on a stable and unstable surface

Exercise or Swiss balls are increasingly being used with conventional resistance exercises. There is little evidence supporting the efficacy of this approach compared to traditional resistance training on a stable surface. Previous studies have shown that force output may be reduced with no change in muscle electromyography (EMG) activity while others have shown increased muscle EMG activity when performing resistance exercises on an unstable surface. This study compared 1RM strength, and upper body and trunk muscle EMG activity during the barbell chest press exercise on a stable (flat bench) and unstable surface (exercise ball). After familiarization, 13 subjects underwent testing for 1RM strength for the barbell chest press on both a stable bench and an exercise ball, each separated by at least 7 days. Surface EMG was recorded for 5 upper body muscles and one trunk muscle from which average root mean square of the muscle activity was calculated for the whole 1RM lift and the concentric and eccentric phases. Elbow angle during each lift was recorded to examine any range-of-motion differences between the two surfaces. The results show that there was no difference in 1RM strength or muscle EMG activity for the stable and unstable surfaces. In addition, there was no difference in elbow range-of-motion between the two surfaces. Taken together, these results indicate that there is no reduction in 1RM strength or any differences in muscle EMG activity for the barbell chest press exercise on an unstable exercise ball when compared to a stable flat surface. Moreover, these results do not support the notion that resistance exercises performed on an exercise ball are more efficacious than traditional stable exercises.     

Electromyographic amplitude ratio of serratus anterior and upper trapezius muscles during modified push-ups and bench press exercises

Imbalance and weakness of the serratus anterior and upper trapezius force couple have been described in patients with shoulder dysfunction. There is interest in identifying exercises that selectively activate these muscles and including it in rehabilitation protocols. This study aims to verify the UT/SA electromyographic (EMG) amplitude ratio, performed in different upper limb exercises and on two bases of support. Twelve healthy men were tested (average age = 22.8 +/- 3.1 years), and surface EMG was recorded from the upper trapezius and serratus anterior using single differential surface electrodes. Volunteers performed isometric contractions over a stable base of support and on a Swiss ball during the wall push-up (WP), bench press (BP), and push-up (PU) exercises. All SEMG data are reported as a percentage of root mean square or integral of linear envelope from the maximal value obtained in one of three maximal voluntary contractions for each muscle studied. A linear mixed-effect model was performed to compare UT/SA ratio values. The WP, BP, and PU exercises showed UT/SA ratio mean +/- SD values of 0.69 +/- 0.72, 0.14 +/- 0.12, and 0.39 +/- 0.37 for stable surfaces, respectively, whereas for unstable surfaces, the values were 0.73 +/- 0.67, 0.43 +/- 0.39, and 0.32 +/- 0.30. The results demonstrate that UT/SA ratio was influenced by the exercises and by the upper limb base of support. The practical application is to show that BP on a stable surface is the exercise preferred over WP and PU on either surfaces for serratus anterior muscle training in patients with imbalance between the UT/SA force couple or serratus anterior weakness.     

Maintenance of EMG activity and loss of force output with instability

Swiss Balls used as a platform for training provide an unstable environment for force production. The objective of this study was to measure differences in force output and electromyographic (EMG) activity of the pectoralis major, anterior deltoid, triceps, latissimus dorsi, and rectus abdominus for isometric and dynamic contractions under stable and unstable conditions. Ten healthy male subjects performed a chest press while supported on a bench or a ball. Unstable isometric maximum force output was 59.6% less than under stable conditions. However, there were no significant differences in overall EMG activity between the stable and unstable protocols. Greater EMG activity was detected with concentric vs. eccentric or isometric contractions. The decreased balance associated with resistance training on an unstable surface may force limb musculature to play a greater role in joint stability. The diminished force output suggests that the overload stresses required for strength training necessitate the inclusion of resistance training on stable surfaces.     

Not all instability training devices enhance muscle activation in highly resistance-trained individuals

The objective of this study was to measure the electromyographic (EMG) activity of the soleus, bicep femoris, rectus femoris, lower abdominal, and lumbosacral erector spinae (LSES) muscles with a variety of (a) instability devices, (b) stable and unstable (Dyna Disc) exercises, and (c) a fatiguing exercise in 16 highly conditioned individuals. The device protocol had participants assume standing and squatting postures while balancing on a variety of unstable platforms (Dyna Disc, BOSU ball, wobble board, and a Swiss ball) and a stable floor. The exercise protocol had subjects performing, static front lunges, static side lunges, 1-leg hip extensions, 1-leg reaches, and calf raises on a floor or an unstable Dyna Disc. For the fatigue experiment, a wall sit position was undertaken under stable and unstable (BOSU ball) conditions. Results for the device experiment demonstrated increased activity for all muscles when standing on a Swiss ball and all muscles other than the rectus femoris when standing on a wobble board. Only lower abdominals and soleus EMG activity increased while squatting on a Swiss ball and wobble board. Devices such as the Dyna Disc and BOSU ball did not exhibit significant differences in muscle activation under any conditions, except the LSES in the standing Dyna Disc conditions. During the exercise protocol, there were no significant changes in muscle activity between stable and unstable (Dyna Disc) conditions. With the fatigue protocol, soleus EMG activity was 51% greater with a stable base. These results indicate that the use of moderately unstable training devices (i.e., Dyna Disc, BOSU ball) did not provide sufficient challenges to the neuromuscular system in highly resistance-trained individuals. Since highly trained individuals may already possess enhanced stability from the use of dynamic free weights, a greater degree of instability may be necessary.     

Activation of the shoulder and arm muscles during axial load exercises on a stable base of support and on a medicine ball

The purpose of this study was to compare SEMG activities during axial load exercises on a stable base of support and on a medicine ball (relatively unstable). Twelve healthy male volunteers were tested (x = 23 ± 7y). Surface EMG was recorded from the biceps brachii, anterior deltoid, clavicular portion of pectoralis major, upper trapezius and serratus anterior using surface differential electrodes. All SEMG data are reported as percentage of RMS mean values obtained in maximal voluntary contractions for each muscle studied. A 3-way within factor repeated measures analysis of variance was performed to compare RMS normalized values. The RMS normalized values of the deltoid were always greater during the exercises performed on a medicine ball in relation to those performed on a stable base of support. The trapezius showed greater mean electric activation amplitude values on the wall-press exercise on a medicine ball, and the pectoralis major on the push-up. The serratus and biceps did not show significant differences of electric activation amplitude in relation to both tested bases of support. Independent of the base of support, none of the studied muscles showed significant differences of electric activation amplitude during the bench-press exercise. The results contribute to the identification of the levels of muscular activation amplitude during exercises that are common in clinical practice of rehabilitation of the shoulder and the differences in terms of type of base of support used.     

Electromyographic response of the abdominal musculature to varying abdominal exercises

This study examined the electromyographic (EMG) response of the upper rectus abdominis (URA), lower rectus abdominis (LRA), internal obliques (IOs), external obliques (EOs), and the rectus femoris (RF) during various abdominal exercises (crunch, supine V-up, prone V-up on ball, prone V-up on slide board, prone V-up on TRX, and prone V-up on Power Wheel). The subjects (n = 21) performed an isometric contraction of the abdominal musculature while performing these exercises. Testing revealed no statistically significant differences between any of the exercises with respect to the EOs, the URA, or the LRA. However, when examining the IO muscle, the supine V-up exercise displayed significantly greater muscle activity than did the slide exercise. In addition, EMG activity of the RF during the crunch was significantly less than in any of the other 5 exercises. These results indicate that when performing isometric abdominal exercises, non-equipment-based exercises stressed the abdominal muscles similarly to equipment-based exercises. Based on the findings of the current study, the benefit of training the abdominal musculature in an isometric fashion using commercial equipment could be called into question.     

Shoulder muscle EMG activity during push up variations on and off a Swiss ball

Background

Surface instability is a common addition to traditional rehabilitation and strength exercises with the aim of increasing muscle activity, increasing exercise difficulty and improving joint proprioception. The aim of the current study was to determine if performing upper body closed kinetic chain exercises on a labile surface (Swiss ball) influences myoelectric amplitude when compared with a stable surface.

Methods

Thirteen males were recruited from a convenience sample of college students. Surface electromyograms were recorded from the triceps, pectoralis major, latissimus dorsi, rectus abdominis and external oblique while performing push up exercises with the feet or hands placed on a bench and separately on a Swiss ball. A push up plus exercise was also evaluated with hands on the support surface.

Results and discussion

Not all muscles responded with an increase in muscle activity. The pectoralis major muscle was not influenced by surface stability. The triceps and rectus abdominis muscles showed increases in muscle activity only when the hands were on the unstable surface. The external oblique muscle was only influenced by surface stability during the performance of the push up plus exercise. No muscle showed a change in activation level when the legs were supported by the Swiss ball instead of the bench.

Conclusion

Muscle activity can be influenced by the addition of surface instability however an increase in muscle activity does not influence all muscles in all conditions. The relationship between the participant's center of mass, the location of the unstable surface and the body part contacting the Swiss ball may be important factors in determining the muscle activation changes following changes in surface stability.

     

Reliability of electromyographic amplitude values of the upper limb muscles during closed kinetic chain exercises with stable and unstable surfaces

The purpose of the present study was to evaluate the intra and interday reliability of surface electromyographic amplitude values of the scapular girdle muscles and upper limbs during 3 isometric closed kinetic chain exercises, involving upper limbs with the fixed distal segment extremity on stable base of support and on a Swiss ball (relatively unstable). Twenty healthy adults performed the exercises push-up, bench-press and wall-press with different effort levels (80% and 100% maximal load). Subjects performed three maximal voluntary contractions (MVC) in muscular testing position of each muscle to obtain a reference value for root mean square (RMS) normalization. Individuals were instructed to randomly perform three isometric contraction series, in which each exercise lasted 6 s with a 2-min resting-period between series and exercises. Intra and interday reliabilities were calculated through the intraclass correlation coefficient (ICC 2.1), standard error of the measurement (SEM). Results indicated an excellent intraday reliability of electromyographic amplitude values (ICC ? 0.75). The interday reliability of normalized RMS values ranged between good and excellent (ICC 0.52–0.98). Finally, it is suggested that the reliability of normalized electromyographic amplitude values of the analyzed muscles present better values during exercises on a stable surface. However, load levels used during the exercises do not seem to have any influence on variability levels, possibly because the loads were quite similar.     

Electromyographic activity of the trunk stabilizers during stable and unstable bench press

The purpose of this study was to investigate the effectiveness of instability training in the recruitment of core stabilizing muscles during dynamic multijoint movement. Surface electromyography (EMG) was measured from 6 muscles (latissimus dorsi, rectus abdominus, internal obliques, erector spinae, and soleus) while subjects performed a 9.1-kg bench press on stable and unstable surfaces. There were 4 exercises in total: (a) stable surfaces for shoulders and feet, (b) upper-body instability, (c) lower-body instability, and (d) dual instability. Five seconds of EMG were recorded during each bench press and were subsequently smoothed with root mean squares calculated for the entire time-series. A repeated-measures analysis of variance (ANOVA) was used to test overall differences between exercise conditions for each muscle. Paired equal variance t-tests with a stepwise Bonferroni correction for multiple contrasts (alpha = 0.05/total number of contrasts) were performed for muscles with significant repeated-measures ANOVA results. The results show significant increases in EMG with increasing instability. Specifically, the dual instability bench press resulted in the greatest mean muscle activation of the 3 stability conditions, with single instability conditions being significantly greater than the stable condition. This pattern of results is consistent with the position that performing the bench press in a progressively unstable environment may be an effective method to increase activation of the core stabilizing musculature, while the upper- and lower-body stabilizers can be activated differentially depending on the mode of instability.     

Electromyographic normalization procedures for determining exercise intensity of closed chain exercises for strengthening the quadriceps femoris muscles

The purpose of this study was to compare the electromyographic (EMG) amplitudes of the quadriceps femoris (QF) muscles during a maximum voluntary isometric contraction (MVIC) to submaximal and maximal dynamic concentric contractions during active exercises. A secondary purpose was to provide information about the type of contraction that may be most appropriate for normalization of EMG data if one wants to determine if a lower extremity closed chain exercise is of sufficient intensity to produce a strengthening response for the QF muscles. Sixty-eight young healthy volunteers (39 female, 29 male) with no lower extremity pain or injury participated in the study. Surface electrodes recorded EMG amplitudes from the vastus medialis obliquus (VMO), rectus femoris (RF), and vastus lateralis (VL) muscles during 5 different isometric and dynamic concentric exercises. The last 27 subjects performed an additional 4 exercises from which a second data set could be analyzed. Maximum isokinetic knee extension and moderate to maximum closed chain exercises activated the QF significantly more than a MVIC. A 40-cm. lateral step-up exercise produced EMG amplitudes of the QF muscles of similar magnitude as the maximum isokinetic knee extension exercises and would be an exercise that could be considered for strengthening the QF muscles. Most published EMG studies of exercises for the QF have been performed by comparing EMG amplitudes during dynamic exercises to a MVIC. This procedure can lead one to overestimate the value of a dynamic exercise for strengthening the QF muscles. We suggest that when studying the efficacy of a dynamic closed chain exercise for strengthening the QF muscles, the exercise be normalized to a dynamic maximum muscle contraction such as that obtained with knee extension during isokinetic testing.     

Reliability of surface EMG measurements over 12 hours.

Bone and muscle are both compromised during long-term space flight. Experiments are, therefore, in progress using surface electromyography (EMG) and joint angle measurements to compare muscle action on earth and in space over complete working days. To date, there is little information on the reliability of such long-term EMG measurements available in the literature. Therefore, the current study determined the reliability and feasibility of using surface EMG over a 12-h interval. Ten young subjects performed standardized isometric exercises at 30% of maximum voluntary effort every 2h throughout a normal working day, which included a period of self-chosen exercise. Surface electrodes remained in place over the biceps brachii (BB), vastus medialis (VM), and gastrocnemius (GN) throughout the day. The normalized integrated EMG for two of the three muscles showed no significant changes during the 12-h period, and only the first observation for VM showed a trend (p<0.1) of differences with three of the other measurement periods. The stability of surface EMG measurements over the 12-h period suggests that this methodology is feasible for use in future long-term EMG studies.     

Trunk muscle electromyographic activity with unstable and unilateral exercises

The purpose of this cross-sectional study was to evaluate the effect of unstable and unilateral resistance exercises on trunk muscle activation. Eleven subjects (6 men and 5 women) between 20 and 45 years of age participated. Six trunk exercises, as well as unilateral and bilateral shoulder and chest presses against resistance, were performed on stable (bench) and unstable (Swiss ball) bases. Electromyographic activity of the upper lumbar, lumbosacral erector spinae, and lower-abdominal muscles were monitored. Instability generated greater activation of the lower-abdominal stabilizer musculature (27.9%) with the trunk exercises and all trunk stabilizers (37.7-54.3%) with the chest press. There was no effect of instability on the shoulder press. Unilateral shoulder press produced greater activation of the back stabilizers, and unilateral chest press resulted in higher activation of all trunk stabilizers, when compared with bilateral presses. Regardless of stability, the superman exercise was the most effective trunk-stabilizer exercise for back-stabilizer activation, whereas the side bridge was the optimal exercise for lower-abdominal muscle activation. Thus, the most effective means for trunk strengthening should involve back or abdominal exercises with unstable bases. Furthermore, trunk strengthening can also occur when performing resistance exercises for the limbs, if the exercises are performed unilaterally.     

Trunk muscle activation during dynamic weight-training exercises and isometric instability activities

The purpose of this study was to examine the extent of activation in various trunk muscles during dynamic weight-training and isometric instability exercises. Sixteen subjects performed squats and deadlifts with 80% 1 repetition maximum (1RM), as well as with body weight as resistance and 2 unstable calisthenic-type exercises (superman and sidebridge). Electromyographic (EMG) activity was measured from the lower abdominals (LA), external obliques (EO), upper lumbar erector spinae (ULES), and lumbar-sacral erector spinae (LSES) muscle groups. Results indicated that the LSES EMG activity during the 80% 1RM squat significantly exceeded 80% 1RM deadlift LSES EMG activity by 34.5%. The LSES EMG activity of the 80% 1RM squat also exceeded the body weight squat, deadlift, superman, and sidebridge by 56, 56.6, 65.5, and 53.1%, respectively. The 80% 1RM deadlift ULES EMG activity significantly exceeded the 80% 1RM squat exercise by 12.9%. In addition, the 80% 1RM deadlift ULES EMG activity also exceeded the body weight squat, deadlift, superman, and sidebridge exercises by 66.7, 65.5, 69.3, and 68.6%, respectively. There were no significant changes in EO or LA activity. Therefore, the augmented activity of the LSES and ULES during 80% 1RM squat and deadlift resistance exercises exceeded the activation levels achieved with the same exercises performed with body weight and selected instability exercises. Individuals performing upright, resisted, dynamic exercises can achieve high trunk muscle activation and thus may not need to add instability device exercises to augment core stability training.     

Force generation performance and motor unit recruitment strategy in muscles of contralateral limbs.

The purpose of the present study was to determine whether the motor unit (MU) recruitment strategy of the agonist and antagonist muscles in the dominant arm differs from that in the non-dominant arm. The median frequency (MF) of the power density spectrum (PDS) of the electromyogram (EMG) was used as a tracking parameter to describe the MU recruitment. In 8 subjects the EMG was recorded from the biceps brachii and triceps brachii of each limb during isometric elbow flexion performed in a ramp fashion. Force was increased from 0 to 100% of the maximum voluntary contraction (MVC) in 3 s following a track displayed on an oscilloscope. When comparing the dominant versus non-dominant arm we found no statistical difference in the MU recruitment pattern of the biceps brachii and the triceps. Because the dominant arm was not always the better performing arm, we grouped the data according to the ability of the subjects to track the ramp signal. In this case we found a statistically significant difference between the better and worse performing arm in the full MU recruitment of the biceps. A more precise and accurate control of the increase in force was obtained when the central nervous system selected a slower and prolonged recruitment of MUs in the agonist muscle.     

Muscle synergy in isometric flexion of the elbow]

A technique was developed for calculating the torque generated by two individual muscles (biceps brachii and brachioradialis) that contribute to the isometric flexion of the elbow. The external torque is the sum of individual torques which are unknown. Each individual torque (CB or CBR) can be related to the corresponding integrated surface EMG (QB or QBR) by means of coefficients (pB or PBR). A block of several equations C = pB QB + pBR QBR is obtained by exploring several experimental conditions. In these conditions, isometric flexion efforts of the elbow were associated to isometric efforts of supination or pronation so as to vary integrated EMG by reciprocal inhibition. By means of a least square method it was possible to know the coefficients PB and PBR. With these coefficients, it was possible to calculate the individual torques generated by the biceps brachii and brachioradialis muscles in each experimental condition.     

Replacing a Swiss ball for an exercise bench causes variable changes in trunk muscle activity during upper limb strength exercises

Background

The addition of Swiss balls to conventional exercise programs has recently been adopted. Swiss balls are an unstable surface which may result in an increased need for force output from trunk muscles to provide adequate spinal stability or balance. The aim of the study was to determine whether the addition of a Swiss ball to upper body strength exercises results in consistent increases in trunk muscle activation levels.

Methods

The myoelectric activity of four trunk muscles was quantified during the performance of upper body resistance exercises while seated on both a stable (exercise bench) and labile (swiss ball) surface. Participants performed the supine chest press, shoulder press, lateral raise, biceps curl and overhead triceps extension. A repeated measures ANOVA with post-hoc Tukey test was used to determine the influence of seated surface type on muscle activity for each muscle.

Results & Discussion

There was no statistically significant (p < .05) difference in muscle activity between surface conditions. However, there was large degree of variability across subjects suggesting that some individuals respond differently to surface stability. These findings suggest that the incorporation of swiss balls instead of an exercise bench into upper body strength training regimes may not be justified based only on the belief that an increase spinal stabilizing musculature activity is inherent. Biomechanically justified ground based exercises have been researched and should form the basis for spinal stability training as preventative and therapeutic exercise training regimes.

Conclusion

Selected trunk muscle activity during certain upper limb strength training exercises is not consistently influenced by the replacement of an exercise bench with a swiss ball.

     

Electromyographic measures of muscle activation and changes in muscle architecture of human elbow flexors during fatiguing contractions.

The study compared changes in intramuscular and surface recordings of EMG amplitude with ultrasound measures of muscle architecture of the elbow flexors during a submaximal isometric contraction. Ten subjects performed a fatiguing contraction to task failure at 20% of maximal voluntary contraction force. EMG activity was recorded in biceps brachii, brachialis, and brachioradialis muscles using intramuscular and surface electrodes. The rates of increase in the amplitude of the surface EMG for the long and short heads of biceps brachii and brachioradialis were greater than those for the intramuscular recordings measured at different depths. The amplitude of the intramuscular recordings from three muscles increased at a similar rate (P = 0.13), as did the amplitude of the three surface recordings from two muscles (P = 0.83). The increases in brachialis thickness (27.7 +/- 5.7 to 30.9 +/- 3.5 mm; P < 0.05) and pennation angle (10.9 +/- 3.5 to 16.5 +/- 4.8 degrees ; P = 0.003) were not associated with the increase in intramuscular EMG amplitude (P > 0.58). The increase in brachioradialis thickness (22.8 +/- 4.8 to 25.5 +/- 3.4 mm; P = 0.0075) was associated with the increase in the amplitude for one of two intramuscular EMG signals (P = 0.007, r = 0.79). The time to failure was more strongly associated with the rate of increase in the amplitude of the surface EMG than that for the intramuscular EMG, which suggests that the surface measurement provides a more appropriate measure of the change in muscle activation during a fatiguing contraction.     

EMG and MMG of agonist and antagonist muscles as a function of age and joint angle.

The aim of this study was to determine the effect of elbow joint position on electromyographic (EMG) and mechanomyographic (MMG) activities of agonist and antagonist muscles in young and old women. Surface EMG and MMG were recorded from the triceps and biceps brachii, and brachioradialis muscles during isometric elbow extensions in young and old women. The measurements were carried out at an optimal joint angle (A(o)), as well as at smaller (A(s) = A(o) - 30 degrees ) and larger (A(l) = A(o) + 30 degrees ) angles. The normalized to force EMG amplitude (RMS-EMG/F) was smaller in old women compared to young in all muscles. The RMS-EMG/F of the triceps brachii muscle was not affected by muscle length while that of the biceps brachii and brachioradialis muscles increased at shortest muscle length in both groups. The normalized to force MMG amplitude (RMS-MMG/F) was smaller in old than in young in the triceps brachii muscle only. There was an increase in RMS-MMG/F with triceps brachii and biceps brachii muscle shortening in both groups, and in the brachioradialis muscle -- in young only. Compared to young, older women exhibited a bigger force fluctuation during maximum voluntary contraction, but these did not contribute significantly to the RMS-MMG. Skinfold thickness accounted for the RMS-EMG/F and RMS-MMG/F differences seen between old and young women in the biceps brachii muscle only. It is concluded that, the EMG and MMG response to muscles length change in agonist and antagonist muscles is generally similar in old and young women but the optimal angle shifts toward a bigger value in older women.     

Isometric squat force output and muscle activity in stable and unstable conditions

The purpose of this study was to assess the effect of stable vs. unstable conditions on force output and muscle activity during an isometric squat. Nine men involved in recreational resistance training participated in the investigation by completing a single testing session. Within this session subjects performed isometric squats either while standing directly on the force plate (stable condition, S) or while standing on inflatable balls placed on top of the force plate (unstable condition, U). Electromyography (EMG) was recorded during both conditions from the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and medial gastrocnemius (G) muscles. Results indicated peak force (PF) and rate of force development (RFD) were significantly lower, 45.6% and 40.5% respectively, in the U vs. S condition (p < or = 0.05). Average integrated EMG values for the VL and VM were significantly higher in the S vs. U condition. VL and VM muscle activity was 37.3% and 34.4% less in U in comparison to S. No significant differences were observed in muscle activity of the BF or G between U and S. The primary finding in this investigation is that isometric squatting in an unstable condition significantly reduces peak force, rate of force development, and agonist muscle activity with no change in antagonist or synergist muscle activity. In terms of providing a stimulus for strength gain no discernable benefit of performing a resistance exercise in an unstable condition was observed in the current study.