Effects of unstable load and unstable surface ontrunk muscles activation and postural control in healthy subjects

Exercise with an unstable load is considered a new training method to activate the core muscles. Research has shown consistency regarding an unstable surface but has not provided comprehensive findings about the effect of an unstable load. The study aimed to examine the impact of an unstable load and unstable surfaces on core muscle activation and postural control during lifting. Thirty-eight participants lifted a load equivalent to 10 % of their body weight under three conditions: a stable load on an unstable surface, a stable load on a stable surface, and an unstable load on a stable surface. The center of pressure (COP) displacement and electromyography activity of abdominal and back extensor muscles were measured during lifting. The results indicated that lifting on an unstable surface activated the lumbar erector spinae and multifidus muscles more than in a stable condition (P<0.05). However, there was no significant difference in the level of thoracic erector spinae muscle activity between the unstable load and unstable surface conditions. The stable condition increased activity in the internal oblique muscle (1.37 times) compared to the unstable conditions. The analysis of postural control revealed that lifting the load on an unstable surface significantly decreased COP displacement in the anteroposterior direction (P<0.05), while holding the load on the unstable surface significantly increased COP displacement in the anteroposterior direction compared to the other conditions. These findings could be valuable for future rehabilitation research, learning appropriate lifting techniques, and setting specific training goals in sports.

Relationship Between Muscle Activity and Force During Suspended Bridge Exercises

CONTEXT

Isometric core stability exercises are commonly used to target muscles of the lumbopelvic-hip complex, including the rectus abdominis (RA) and erector spinae (ES). These exercises can be implemented in rehabilitation protocols to increase muscle strength and endurance. Difficulty can be progressed by modifying the base of support or adding an unstable element. Load cells can be affixed to suspension training devices to measure force exerted through the straps during exercise. The primary purpose of this study was to assess the relationship between activity of the RA and ES to force measured through a load cell fixed to suspension straps during bilateral and unilateral suspended bridge exercises.

DESIGN

Forty asymptomatic, active individuals completed a single laboratory visit.

METHODS

Participants completed 2 bilateral suspended bridges and 2 unilateral suspended bridges held to failure. Surface electromyography sensors were placed over the bilateral RA and ES to quantify muscle activity (% maximum voluntary isometric contraction). A load cell was affixed to the suspension straps to measure force exerted through the straps throughout the duration of the exercise. Pearson correlations were used to determine relationships between force and muscle activity of the RA and ES throughout exercise duration.

RESULTS

Force was negatively related to RA muscle activity in bilateral suspended bridges (r = -.735 to -.842, P < .001) and unilateral suspended bridges (r = -.300 to -.707, P = .002 to <.001). Force had a positive relationship with ES muscle activity in bilateral suspended bridges (r = .689 to .791, P < .001) and unilateral suspended bridges (r = .418 to .448, P < .001).

CONCLUSIONS

Suspended bridge exercises can be a valuable tool to target posterior abdominal musculature such as the ES to contribute to core stability and endurance. Load cells can be applied during suspension training to quantify the interaction between individuals and the exercise equipment.

Exploring of two different equated instability resistance training programs on measure of physical fitness and lower limb asymmetry in pre-pubertal weightlifters

BACKGROUND

Although previous research in pediatric populations has reported performance enhancements following instability resistance training, the effects of different volumes on measures of balance, strength and power and lower limb asymmetry remain unclear.

OBJECTIVE

To compare the effect of two 8-week instability resistance training programs (IRT1: 2 sets x 8 repetitions, 20% one-repetition maximum (1RM); IRT2: 2 sets x 4 repetitions, 40% 1RM) in balance (center of pressure displacements), 1RM, single-leg jumps, and inter-limb asymmetry of prepubescent weightlifters.

METHODS

Thirty-two male athletes (10.94 ± 0.47 yrs, 17.05 ± 0.14 kg/m², and 6.44 ± 0.93% bodyfat) voluntarily participated and combined IRT (front and back squat, lunge, and deadlift) with their usual weightlifting training. Nonparametric tests evaluated the differences between pre- and post-intervention.

RESULTS

Significant improvements were encountered in all the variables for both groups (effect sizes [ES] from 0.46 to 2.60), except the inter-limb asymmetry and the velocity of displacement of the center of pressure, which did not improve in IRT2. It is also worth highlighting that in the single-leg jumps and center of pressure displacements, whereas no significant differences were observed between IRT1 and IRT2 in the baseline, significant differences appeared in the follow-up measurements.

CONCLUSION

IRT combined with weight-lifting training improves prepubescent weightlifters' performance; therefore, strength and conditioning coaches may consider including unstable devices with low loads into an overall conditioning program and warm-ups for prepuberal male weightlifters to promote their physical fitness and potentially decrease inter-limb asymmetry.

TRIAL REGISTRATION

This study does not report results related to healthcare interventions using human participants; therefore, it was not prospectively registered.

How Does Instability Affect Bench Press Performance? Acute Effect Analysis with Different Loads in Trained and Untrained Populations

(I) The execution of different sports involves a significant number of throws, jumps, or direction changes, so the body must be as stable as possible while performing a specific action. However, there is no classification of unstable devices and their influence on performance variables. Furthermore, the effect on athletes’ experience using instability is unknown. (II) The aim of this study was to analyze the power and speed parameters in bench press with different loads and unstable executions: (1) stable (SB), (2) with asymmetric load (AB), (3) with unstable load (UB), (4) on fitball (FB) and (5) on a Bosu® (BB). A total of 30 male participants (15 trained and 15 untrained) were evaluated for mean propulsive speed (MPS), maximum speed (MS), and power (PW) with different types of external load: a low load (40% of 1RM), medium load (60% of 1RM), and high load (80% of 1RM) in each condition. Variables were measured with an inertial dynamometer. (III) The best data were evidenced with SB, followed by AB (3–12%), UB (4–11%), FB (7–19%), and BB (14–23%). There were no differences between groups and loads (p > 0.05) except in the case of MS with 60% 1RM, where trained participants obtained 4% better data (p < 0.05). (IV) Executions with implements and equipment such as fitball and Bosu® do not seem to be the most recommended when the objective is to improve power or execution speed. However, situations where the load is unstable (AB and UB) seem to be a good alternative to improve stabilization work without high performance. Furthermore, experience does not seem to be a determining factor.

Assessment of the Speed and Power of Push-Ups Performed on Surfaces with Different Degrees of Instability

(I) Training in unstable conditions, with different elements, platforms, or situations, has been used because there is a significant increase in muscle activation, balance, proprioception, and even sports performance. However, it is not known how the devices used are classified according to performance variables, nor the differences according to instability experience. (II) This study aims to analyze the differences in power and speed in push-ups with different situations of instability in trained and untrained male subjects. Power and speed in push-up exercise were analyzed in 26 untrained and 25 trained participants in 6 different situations (one stable and five unstable) (1) stable (PS), (2) monopodal (PM), (3) rings (PR), (4) TRX^® (PT), (5) hands-on Bosu^® (PH) (6) feet on Bosu^® (PF). The variables were analyzed using a linear position transducer. (III) The best data were evidenced with PS, followed by PR, PM, PT, PH and PF. The trained subjects obtained better results in all the conditions analyzed in mean and maximum power and speed values (p < 0.001). The decrease in these variables was significantly greater in the untrained subjects than in the trained subjects in the PR situation (8% and 18% respectively). In PF there were differences between groups (p < 0.001), reaching between 32-46% in all variables. The difference between the two groups was notable, varying between 12-58%. (IV) The results showed a negative and progressive influence of instability on power and speed in push-ups. This suggests that instability should be adapted to the subject's experience and is not advisable in untrained subjects who wish to improve power.

The Effect of Aquabag Use on Muscle Activation in Functional Strength Training

Context: Although training with an aquabag (AB) has gained popularity, there is a lack of evidence of its effect. This study wanted to evaluate the effect of AB implementation on muscle activity of core and lower limb muscles during 3 functional exercises. Design: Cross-sectional observational study. Methods: Twenty healthy subjects performed a squat, lunge, and step-up, while using a stick and an AB. Surface electromyography signals were recorded from the trunk, pelvis, and thigh muscles in the dominant leg. Linear-mixed models were used to analyze the normalized surface electromyography signals. Results: Results demonstrated a significant increase in muscle activity of the back muscles during all 3 exercises (P < .001 to P = .003), abdominals during squat (P = .034) and step-up (P = .046), hamstrings during lunge (P = .008) and step-up (P = .008), and gluteal muscles during lunge (P < .001 and P = .010, respectively). Conclusions: These results indicate that an AB promotes functional strength training by demanding compensatory/additional activity of both stabilizing muscles (specifically in the core and pelvis regions) and prime movers of the lower limb. The authors recommend the use of an AB to enhance training and rehabilitation effects.

Stable to unstable differences in force-velocity-power profiling during chest presses and squats

Despite several studies investigating the effect of instability resistance exercises on neuromuscular performance, the force-velocity-power characteristics of muscles involved in lifting tasks and the underlying mechanisms have not been fully explored. This study investigates power-velocity and force-velocity relationships during resistance exercises performed on stable and unstable surfaces with different weights. A group of 63 physically active young men performed chest presses on the bench and Swiss ball, and squats on the firm surface and BOSU ball with weights from 20 kg to at least 85% of one-repetition maximum. Peak and/or mean values of power, velocity and force were analyzed. Results showed significantly lower peak power and force during chest presses on the Swiss ball as opposed to the bench at lower velocities (147.6 W and 176.0 N at 1.1 m·s^-1, 108.7 W and 126.4 N at 1.3 m·s^-1, 112.0 W and 72.7 N at 1.5 m·s^-1; all at p < 0.01). Their values produced at lower velocities were also significantly lower during squats on the BOSU ball when compared to the firm surface (232.2 W and 257.1 N at 1.1 m·s^-1, 228.2 W and 173.3 N at 1.2 m·s^-1, 245.1 W and 156.8 N at 1.3 m·s^-1, 254.5 W and 113.5 N at 1.4 m·s^-1; all at p < 0.05). These significant differences between power produced during stable and unstable resistance exercises at lower velocities (or at higher loads) have to be taken into account in sports that require production of a high force in a short time. Because of the variable loading patterns under unstable conditions, it is necessary to quantify the optimal exercise load for each individual athlete.

Comparison of Isolated Lumbar Extension Strength in Competitive and Noncompetitive Powerlifters, and Recreationally Trained Men

ABSTRACT

Androulakis-Korakakis, P, Gentil, P, Fisher, JP, and Steele, J. Comparison of isolated lumbar extension strength in competitive and noncompetitive powerlifters, and recreationally trained men. J Strength Cond Res 35(3): 652-658, 2021-Low-back strength has been shown to significantly impact performance in a plethora of sports. Aside from its effect on sport performance, low-back strength is strongly associated with low-back pain. A sport that heavily involves the lower-back musculature is powerlifting. This study looked to compare isolated lumbar extension (ILEX) strength in competitive and noncompetitive powerlifters, and recreationally trained men. Thirteen competitive powerlifters (CPL group; 31.9 ± 7.6 years; 173.4 ± 5.5 cm; 91.75 ± 18.7 kg), 10 noncompetitive powerlifters (NCPL group; 24 ± 3.5 years; 179 ± 4.8 cm; 92.39 ± 15.73 kg), and 36 recreationally trained men (RECT group; 24.9 ± 6.5 years; 178.5 ± 5.2 cm; 81.6 ± 10.0 kg) were tested for ILEX. Isolated lumbar extension strength was measured at every 12° throughout subject's full range of motion (ROM) and expressed as the following: "strength index (SI)" calculated as the area under a torque curve from multiple angle testing, average torque produced across each joint angle (AVG), and maximum torque produced at a single angle (MAX). Deadlift and squat strength were measured using 1 repetition maximum for the competitive and noncompetitive powerlifters. The following powerlifting characteristics were recorded for the competitive and noncompetitive powerlifters: primary deadlift stance, primary squat bar position, use of belt, use of performance-enhancing drugs, and use of exercises to target the lower-back musculature. Significant between-group effects were found for subject characteristics (age, stature, body mass, and ROM). However, analysis of covariance with subject characteristics as covariates found no significant between-group effects for SI (p = 0.824), AVG (p = 0.757), or MAX (p = 0.572). In conclusion, this study suggests that powerlifting training likely has little impact on conditioning of the lumbar extensors.

Different Gymnastic Balls Affect Postural Balance Rather Than Core-Muscle Activation: A Preliminary Study

Background: In proprioceptive training, unstable devices produce multidirectional perturbations that must be counterbalanced by the postural control systems and core-muscle activation. We investigated whether different sizes and shapes of three gymnastic balls could affect core-muscle activation and postural balance when performing the same exercise. Methods: Eleven young healthy subjects were assessed on the balls, assuming two body postures (bipedal seated and unipedal seated) and performing a dynamic exercise. Two balls were spherical with different diameters, and one was ovoid. Postural balance and muscle activation were assessed through center of pressure (CoP)-related parameters and surface electromyography. Results: Statistical analysis showed a significant effect of the gymnastic balls (p < 0.001) and the body postures (p < 0.001) for the CoP-related parameters, with the ovoid shape and the bipedal sitting representing the easiest conditions. Core-muscle activation was affected only by body postures, with a higher activation in the unipedal sitting (p < 0.01). In the dynamic exercise, significant differences were only detected for the CoP-related parameters (p < 0.001). Conclusions: The shapes and sizes of the gymnastic balls produced different degrees of destabilization under the same body posture but left the core-muscle activation unaltered. In the dynamic exercise, the conformation of the balls did not represent the main determinant in producing destabilizing effects.

Effect of Unstable Loads on Stabilizing Muscles and Bar Motion During the Bench Press

ABSTRACT

Lawrence, MA, Ostrowski, SJ, Leib, DJ, and Carlson, LA. Effect of unstable loads on stabilizing muscles and bar motion during the bench press. J Strength Cond Res 35(2S): S120-S126, 2021-Unstable loads are anecdotally used to increase muscle stabilizer strength and utilization; however, there is little evidence to support these claims. Twelve male powerlifters (age 28.6 ± 5.2 years, body mass 105.6 ± 14.5 kg, lifting experience 9.8 ± 6.0 years, and bench press 5 repetition maximum [5RM] 133.6 ± 30.9 kg) pressed their 5RM in one stable condition with a standard barbell, and 3 unstable conditions using a flexible barbell with weights suspended from elastic bands. Mean integrated muscle activity for each repetition of the stabilizers and prime movers were measured. A Lyapunov exponent and sample entropy indicated unstable loads were less predictable and more variable in the superior/inferior direction, thus more challenging to control, despite decreased loads. The main finding was increased bicep activity in all unstable conditions (light bands and plates, +57%; mini bands and plates, +67%; and mini bands and kettlebells, +88%). Although less weight was used in the unstable 5RMs, most stabilizer muscle activity was not different between conditions, suggesting that the amount of weight used during unstable load training (up to 32.3% less load) may be limited by the ability of stabilizer muscles to control the load.

Effects on Strength, Power and Speed Execution Using Exercise Balls, Semi-Sphere Balance Balls and Suspension Training Devices: A Systematic Review

Research in instability has focused on the analysis of muscle activation. The aim of this systematic review was to analyse the effects of unstable devices on speed, strength and muscle power measurements administered in the form of controlled trials to healthy individuals in adulthood. A computerized systematic literature search was performed through electronic databases. According to the criteria for preparing systematic reviews PRISMA, nine studies met the inclusion criteria. The quality of the selected studies was evaluated using STROBE. The average score was 14.3 points, and the highest scores were located in ‘Introduction’ (100%) and ‘Discussion’ (80%). There is great heterogeneity in terms of performance variables. However, instability seems to affect these variables negatively. The strength variable was affected to a greater degree, but with intensities near to the 1RM, no differences are observed. As for power, a greater number of repetitions seems to benefit the production of this variable in instability in the upper limb. Instability, in comparison to a stable condition, decreases the parameters of strength, power, and muscular speed in adults. The differences shown are quite significant in most situations although slight decreases can be seen in certain situations.

Clinical reasoning framework for thoracic spine exercise prescription in sport: a systematic review and narrative synthesis

BACKGROUND

The thoracic spine is critical for athletic kinetic chain functioning yet widely overlooked in terms of specific evidenced-based exercise prescription. Thoracic mobility, motor control and strength are required to optimise performance in sport and minimise excessive load/stress on other components of the kinetic chain.

OBJECTIVE

To identify and evaluate mobility, motor control, work capacity and strength thoracic exercises for use in athletes.

DESIGN

Systematic review involving expert reviewers at key stages: searches and screening (n=1), eligibility, evaluation, data extraction and evaluation (n=3). Key databases and social media sources were searched to 16 August 2019. Eligible exercises were thoracic exercises to promote mobility, motor control, work capacity and strength. A narrative synthesis enabled an outcome-based classification of exercises, with level of evidence of individual sources informing overall level of evidence for each outcome (Oxford Centre for Evidence-based Medicine).

RESULTS

From 2348 sources (social media, database searches and other sources), 38 exercises were included. Sources included images, video clips and written descriptions of exercises. Exercises targeting all planes of motion were evaluated and classified according to outcome. Exercises comprised functional and non-functional exercises for mobility (n=9), work capacity (n=15), motor control (n=7) and strength (n=7). Overall level of evidence for each outcome was level 5.

CONCLUSION

This synthesis and evaluation of exercises has captured the scope of thoracic exercises used in 'practice'. Evaluation against an expert-derived outcome-based classification provides practitioners with a framework to facilitate exercise prescription. Evaluation of validity and effectiveness of exercises on outcomes is now required.

Electromyographic activity in deadlift exercise and its variants. A systematic review

The main purpose of this review was to systematically analyze the literature concerning studies which have investigated muscle activation when performing the Deadlift exercise and its variants. This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Statement (PRISMA). Original studies from inception until March 2019 were sourced from four electronic databases including PubMed, OVID, Scopus and Web of Science. Inclusion criteria were as follows: (a) a cross-sectional or longitudinal study design; (b) evaluation of neuromuscular activation during Deadlift exercise or variants; (c) inclusion of healthy and trained participants, with no injury issues at least for six months before measurements; and (d) analyzed "sEMG amplitude", "muscle activation" or "muscular activity" with surface electromyography (sEMG) devices. Major findings indicate that the biceps femoris is the most studied muscle, followed by gluteus maximus, vastus lateralis and erector spinae. Erector spinae and quadriceps muscles reported greater activation than gluteus maximus and biceps femoris muscles during Deadlift exercise and its variants. However, the Romanian Deadlift is associated with lower activation for erector spinae than for biceps femoris and semitendinosus. Deadlift also showed greater activation of the quadriceps muscles than the gluteus maximus and hamstring muscles. In general, semitendinosus muscle activation predominates over that of biceps femoris within hamstring muscles complex. In conclusion 1) Biceps femoris is the most evaluated muscle, followed by gluteus maximus, vastus lateralis and erector spinae during Deadlift exercises; 2) Erector spinae and quadriceps muscles are more activated than gluteus maximus and biceps femoris muscles within Deadlift exercises; 3) Within the hamstring muscles complex, semitendinosus elicits slightly greater muscle activation than biceps femoris during Deadlift exercises; and 4) A unified criterion upon methodology is necessary in order to report reliable outcomes when using surface electromyography recordings.

A Biomechanical Analysis of the Effects of Bouncing the Barbell in the Conventional Deadlift

Krajewski, K, LeFavi, R, and Riemann, B. A biomechanical analysis of the effects of bouncing the barbell in the conventional deadlift. J Strength Cond Res 33(7S): S70-S77, 2019-The purpose of this study is to analyze biomechanical differences between the bounce and pause styles of deadlifting. Twenty physically active males performed deadlifts at their 75% one-repetition maximum testing using both pause and bounce techniques in a within-subjects randomized study design. The average peak height the barbell attained from the 3 bounce style repetitions was used to compute a compatible phase for analysis of the pause style repetitions. Net joint moment impulse (NJMI), work, average vertical ground reaction force (vGRF), vGRF impulse, and phase time were computed for 2 phases, liftoff to peak barbell height and the entire ascent. Additionally, the ankle, knee, hip, and trunk angles at the location of peak barbell bounce height were computed. During the liftoff to peak barbell height phase, although each of the joints demonstrated significantly less NJMI and work during the bounce style, the hip joint was impacted the most. The average vGRF was greater for the bounce; however, the vGRF impulse was greater for the pause. The NJMI results for the ascent phase were similar to the liftoff to peak barbell height phase, whereas work was significantly less for the bounce condition compared with the pause condition across all 3 joints. Strength and conditioning specialists using the deadlift should be aware that the bounce technique does not allow the athlete to develop maximal force production in the early portion of the lift. Further analyses should focus on joint angles and potential vulnerability to injury when the barbell momentum generated from the bounce is lost.

Muscle activity of Bulgarian squat. Effects of additional vibration, suspension and unstable surface

Practitioners of strength and conditioning are increasingly using vibration and unstable environments to enhance training effects. However, little evidence has been found comparing the use of suspension devices and vibratory platforms used in the Bulgarian squat. The purpose of this cross-sectional study was to examine the effect of suspension devices (TRX®), unstable surfaces (BOSU®), and vibration plates on muscle activity and force during the Bulgarian squat. Twenty physically active male students (age = 24.40 ± 3.63 years) performed a set of five repetitions of Bulgarian squats, suspended lunges, suspended lunges-BOSU, suspended lunges-Vibro30, and suspended lunges-Vibro40 (vibration 30 Hz or 40 Hz and 4 mm of amplitude). A randomized within-subject design was used to compare leg muscle activity, vertical ground reaction forces, and force exerted on the strap across the five exercises. Results showed no significant differences in muscle activity between the Bulgarian squat and suspended lunge (p = 0.109, d = 2.84). However, the suspended lunge significantly decreased muscle activation compared to the suspended lunge-BOSU (p = 0.012, d = 0.47), suspended lunge-Vibro30 (p = 0.001, d = 1.26), and suspended lunge-Vibro40 (p = 0.000, d = 1.51). Likewise, the Bulgarian squat achieved lower activity than the suspended lunge-Vibro40 (p = 0.010, d = 0.96). The force on the strap significantly decreased in the suspended lunge-BOSU compared to the suspended lunge-Vibro30 (p = 0.009, d = 0.56). The suspended lunge achieved higher front leg force production than the Bulgarian squat (p = 0.006, d = 0.48). In conclusion, leaning the rear leg on a suspension device does not provoke an increase in the activation of the front leg during the Bulgarian squat but increases the vertical ground reaction forces. Thus, the use of unstable surfaces or vibration plates for the front leg increased muscular activity when performing a suspended lunge.

An electromyographic and kinetic comparison of conventional and Romanian deadlifts

Background/objective

Significant biomechanical differences were found among deadlift variations. However, little is known about the differences between the conventional and the Romanian deadlifts. Therefore, the purpose of this study was to determine which deadlift technique is a better training protocol between the conventional and the Romanian deadlifts as indicated by the greater demand in muscle activities and joint kinetics.

Methods

21 males performed each deadlift with 70% of the Romanian deadlift one repetition maximum (1RM) determined using a 1RM testing. Myoelectric activities of the rectus femoris, biceps femoris, and gluteus maximus and lower extremity net joint torque (NJT) were compared. The variables were extracted through an electromyography system (EMG) and a three-dimensional motion analysis. The EMG values were normalized to the peak EMG activation from a submaximal non-isometric voluntary contraction. A two-way repeated measures analysis of variance was conducted for statistical analysis. The level of significance was set at 0.05.

Results

Significantly greater normalized EMG values were found from the rectus femoris and gluteus maximus (58.57 ± 13.73 and 51.52 ± 6.08 %peak) of the conventional deadlift than those of the Romanian deadlift (25.26 ± 14.21 and 46.88 ± 7.39 %peak). The conventional deadlift indicated significantly greater knee and ankle NJTs (0.21 ± 0.13 and −0.33 ± 0.08 Nm/kg cm) than those of the Romanian deadlift (−0.28 ± 0.1 and −0.29 ± 0.06 Nm/kg cm).

Conclusion

The conventional deadlift would be a better technique for training the rectus femoris and gluteus maximus than the Romanian deadlift as indicated by the greater EMG and NJT values.

Shod vs. Barefoot Effects on Force and Power Development During a Conventional Deadlift

Hammer, ME, Meir, RA, Whitting, JW, and Crowley-McHattan, ZJ. Shod vs. barefoot effects on force and power development during a conventional deadlift. J Strength Cond Res 32(6): 1525-1530, 2018-The kinetics of a conventional deadlift in shod (S) vs. unshod (US) footwear conditions in 10 male participants (mean ± SD, age = 27.0 ± 5.8 years; body mass = 78.7 ± 11.5 kg; height = 175.8 ± 8.2 cm; 1 repetition maximum [1RM] deadlift = 155.8 ± 25.8 kg) was assessed in 2 testing sessions. A counterbalanced, cross-over experimental design was used with different loads (60 and 80% 1RM). Four sets of 4 repetitions were prescribed per session with 2 sets per shoe and with each shoe condition involving 1 set per load. Peak vertical force (PF), rate of force development (RFD), time to peak force (TPF), anterior-posterior (COP-AP) and mediolateral (COP-ML) center of pressure excursion, and barbell peak power data were recorded during all repetitions. Except for RFD (F = 6.389; p = 0.045; ηp = 0.516) and ML-COP (F = 6.696; p = 0.041; ηp = 0.527), there were no other significant main effects of shoe. There were significant main effects of load for PF (p ≤ 0.05), COP-AP (p = 0.011), TPF (p = 0.018), and COP-AP (p = 0.011). There were no significant interactions found between session, shoe, and load (p range from 0.944 to 0.086). Although the US condition may have produced changes in RFD and ML-COP compared with the shod condition, there is only limited evidence in the current study to support this lifting technique for the conventional deadlift. Further investigation is required to clarify any possible implications of this result and its benefit to lifters.

Core Muscle Activation During Unstable Bicep Curl Using a Water-Filled Instability Training Tube

Glass, SC, Blanchette, TW, Karwan, LA, Pearson, SS, O'Neil, AP, and Karlik, DA. Core muscle activation during unstable bicep curl using a water-filled instability training tube. J Strength Cond Res 30(11): 3212-3219, 2016-The purpose of this study was to assess compensatory muscle activation created during a bicep curl using a water-filled, unstable lifting tube. Ten men (age = 21 ± 1.6 years, height = 180.0 ± 3.3 cm, mass = 87.4 ± 15.0 kg) and 10 women (age = 19.6 ± 1.3 years, height = 161.4 ± 12.0 cm, mass = 61.2 ± 7.4 kg) completed bicep curls using an 11.4-kg tube partially filled with water during a 50% open-valve, 100% open, and control setting. Subjects completed 8 repetitions within each condition with integrated electromyographic signal (converted to percent maximal voluntary contraction) of the bicep, deltoid, rectus abdominus, and paraspinal muscles measured. Compensatory activation was determined using the natural log of coefficient of variation across concentric (CON) and eccentric (ECC) contractions. There were no differences between gender for any condition. Significant variability was seen across treatments for paraspinal muscles for CON and ECC at 50% (CON LnCV = 3.13 ± 0.56%, ECC LnCV = 3.34 ± 0.58%) and 100% (CON = 3.24 ± 0.34%, ECC = 3.46 ± 0.35%) compared with control (CON = 2.59 ± 0.47%, ECC = 2.80 ± 0.61%). Deltoid variability was greater at the 100% open setting (CON = 3.51 ± 0.53%, ECC = 3.56 ± 0.36%) compared with control (CON = 2.98 ± 0.35%, ECC = 2.97 ± 0.45%). The abdominal CON 100% showed variability (3.02 ± 0.47%) compared with control (2.65 ± 0.43%). Bicep activation remained unvaried. Compensatory activation of postural muscles contribute to postural stability. This device may be a useful tool for neuromuscular training leading to improved stability and control.

Force production during squats performed with a rotational resistance device under stable versus unstable conditions

[Purpose] Force production during a squat action on a rotational resistance device (RRD) under stable and unstable conditions. [Subjects and Methods] Twenty-one healthy males were asked to perform six sets of six repetitions of squats on an RRD on either stable or unstable surfaces. The stable and unstable sets were performed on different days. Muscular outputs were obtained from a linear encoder and a strain gauge fixed to a vest. [Results] Overall, the results showed no significant differences for any of the dependent variables across exercise modes. Force_mean outputs were higher in the concentric phase than in the eccentric phase for each condition, but there were no differences in velocity, time or displacement. The force_peak was similar in the eccentric and concentric phases of movement under both stable and unstable conditions. There were no significant differences in force_mean between sets per condition or between conditions. [Conclusion] These results suggest that performing squats with a RRD achieves similar force_mean and force_peak under stable and unstable conditions. The force_peak produced is also similar in concentric and eccentric phases.

A Comparison of the Effect of Kettlebell Swings and Isolated Lumbar Extension Training on Acute Torque Production of the Lumbar Extensors

The aim of this study was to use a fatigue response test to measure the muscular fatigue (defined as a reduction in torque production) sustained by the lumbar extensors after a single set of kettlebell swings (KBS) in comparison with isolated lumbar extensions (ILEX) and a control condition (CON). The purpose of which is to measure the physiological response of KBS against an already established modality. Subsequent data provide insight of the efficacy of kettlebells swings in strengthening the lumbar muscles and lower back pain treatment. Eight physically active males participated in a repeated measures design where participants completed all conditions. There were statistically significant reductions in maximal torque, reported as strength index (SI), after both KBS and ILEX exercise. A statistically significant difference was found for reductions in maximal torque between CON and both KBS (p = 0.005) and ILEX (p = 0.001) and between KBS and ILEX (p = 0.039). Mean reduction and effect sizes were -1824 ± 1127.12 (SI) and -1.62 for KBS and -4775.6 ± 1593.41 (SI) and -3.00 for ILEX. In addition, a statistically significant difference was found between KBS and ILEX for rate of perceived exertion (p = 0.012). Data suggest that both KBS and ILEX were able to fatigue the lumbar extensors. Isolated lumbar extension was able to generate a greater level of fatigue. However, contrary to previous research, the KBS was able to elicit a physiological response, despite the lack of pelvic restraint supporting the potential to strengthen the lumbar extensors.

Muscle activation during push-ups performed under stable and unstable conditions

Background/Objective

The purpose of this study was to analyze muscle activation when performing push-ups under different stability conditions.

Methods

Physically fit young male university students (N = 30) performed five push-ups under stable conditions (on the floor) and using four unstable devices (wobble board, stability disc, fitness dome, and the TRX Suspension Trainer). The push-up speed was controlled using a metronome, and the testing order was randomized. The average amplitudes of the electromyographic (EMG) root mean square of the anterior deltoid (DELT), serratus anterior (SERRA), lumbar multifidus (LUMB), and rectus femoris (FEM) were recorded. The electromyographic signals were normalized to the maximum voluntary isometric contraction (MVIC).

Results

No significant differences were found for the DELT [F(4,112) = 1.978; p = 0.130] among the conditions. However, statistically significant differences were found among the different conditions for the SERRA [F(4,60) = 17.649; p < 0.001], LUMB [F(4,76) = 12.334; p < 0.001], and FEM [F(4,104) = 24.676; p < 0.001] muscle activation. The suspended device was the only condition that elicited higher LUMB and FEM activation compared to the other conditions. Push-ups performed on the floor showed lower SERRA activation than those performed with all unstable devices.

Conclusion

Not all unstable devices enhance muscle activation compared to traditional push-ups.

Core muscle activity in a series of balance exercises with different stability conditions

Literature that provides progression models based on core muscle activity and postural manipulations is scarce. The purpose of this study was to investigate the core muscle activity in a series of balance exercises with different stability levels and additional elastic resistance. A descriptive study of electromyography (EMG) was performed with forty-four healthy subjects that completed 12 exercises in a random order. Exercises were performed unipedally or bipedally with or without elastic tubing as resistance on various unstable (uncontrolled multiaxial and uniaxial movement) and stable surfaces. Surface EMG on the lumbar multífidus spinae (LM), thoracic multífidus spinae (TM), lumbar erector spinae (LE), thoracic erector spinae (TE) and gluteus maximus (GM), on the dominant side of the body were collected to quantify the amount of muscle activity and were expressed as a % of the maximum voluntary isometric contraction (MVIC). Significant differences (p<.001) were found between exercises. The three unipedal standing exercises with additional elastic resistance generated the greatest EMG values, ranging from 19% MVIC to 30% MVIC. Postural manipulations with additional elastic resistance and/or unstable devices increase core muscle activity. An adequate exercise progression based on global core EMG could start with seated positions, progressing to bipedal standing stance (i.e., from either multiaxial or stable surface to uniaxial surface). Following this, unipedal standing positions may be performed (i.e., from either multiaxial or stable surface to uniaxial surface) and finally, elastic resistance must be added in order to increase EMG levels (i.e., from stable surface progressing to any of the used unstable surfaces).

Examination of a lumbar spine biomechanical model for assessing axial compression, shear, and bending moment using selected Olympic lifts

BACKGROUND/AIMS

Loading during concurrent bending and compression associated with deadlift, hang clean and hang snatch lifts carries the potential for injury to the intervertebral discs, muscles and ligaments. This study examined the capacity of a newly developed spinal model to compute shear and compressive forces, and bending moments in lumbar spine for each lift.

METHODS

Five male subjects participated in the study. The spine was modeled as a chain of rigid bodies (vertebrae) connected via the intervertebral discs. Each vertebral reference frame was centered in the center of mass of the vertebral body, and its principal directions were axial, anterior-posterior, and medial-lateral.

RESULTS

The results demonstrated the capacity of this spinal model to assess forces and bending moments at and about the lumbar vertebrae by showing the variations among these variables with different lifting techniques.

CONCLUSION

These results show the model's potential as a diagnostic tool.

Comparing one repetition maximum and three repetition maximum between conventional and eccentrically loaded deadlifts

This study determined if an eccentrically loaded deadlift yields a higher 1 repetition maximum (1RM) and 3RM than a conventional deadlift and if the 1RM conventional and eccentrically loaded deadlift can be accurately estimated from the 3RM (3RM = 93% of 1RM). Division 1 football players (n = 15; 20.3 ± 1.9 years; 95.8 ± 18.2 kg; 184.4 ± 6.6 cm) participated. Deadlift 1RM and 3RM were measured in the conventional and eccentrically loaded deadlift. Dependent t-tests showed no significant difference between the 3RM and 1RM conventional deadlift and the 3RM and 1RM eccentrically loaded deadlift (p = 0.30 and p = 0.20, respectively). Pearson correlation between the 1RM conventional deadlift estimate and 1RM conventional deadlift actual was r = 0.91 (p ≤ 0.01); a dependent t-test indicated the 1RM conventional deadlift estimate was significantly less than the 1RM conventional deadlift actual (p = 0.007). Pearson correlation between the 1RM eccentrically loaded deadlift estimate and 1RM eccentrically loaded deadlift actual was r = 0.84 (p ≤ 0.01); a dependent t-test indicated the 1RM eccentrically loaded deadlift estimate was nearly significantly less than the 1RM eccentrically loaded deadlift actual (p = 0.061). Results suggest that conventional and eccentrically loaded deadlifts may be interchangeable within a training program; this may elicit the benefits of using a broader variety of ground-based multijoint compound movements in an athlete's strength and power training. Additionally, because of differences between predicted and actual 1RM scores in the deadlift, strength coaches should prioritize actual 1RM testing of their athletes to optimize deadlift training loads across the RM continuum.

Muscle activation in young men during a lower limb aquatic resistance exercise with different devices

Little research has been reported on the effects of using different devices with resistance exercises in a water environment. This study compared muscular activation of lower extremity and core muscles during leg adduction performed at maximum velocity with drag and floating devices of different sizes. A total of 24 young men (mean age 23.20 ± 1.18 years) performed 3 repetitions of leg adduction at maximum velocity using 4 different devices (ie, large/small and drag/floating). The maximum amplitude of the electromyographic root mean square of the adductor longus, rectus abdominis, external oblique on the dominant side, external oblique on the nondominant side, and erector lumbar spinae were recorded. Electromyographic signals were normalized to the maximum voluntary isometric contraction (MVIC). Unexpectedly, no significant (P > 0.05) differences were found in the neuromuscular responses among the different devices used; the average activation of agonist muscle adequate for neuromuscular conditioning was 40.95% of MVIC. In addition, external oblique activation is greater on the contralateral side to stabilize the body (average, 151.74%; P < 0.05). Therefore, if maximum muscle activation is required, the kind of device is not relevant. Thus, the choice should be based on economic factors.