Instability in resistance training

Objective: We verified the effect of 10 weeks of structured FT grouped by muscular actions (GFT) or alternating actions (AFT) on scapular and lumbar-pelvic girdle stability. Method: One hundred and twenty adults (60 men; 60 women) were allocated into three groups, GFT (n = 40) that performed the actions in sequence (squat-squat-pull-pull), AFT (n = 40) that performed alternate actions (squat-pull-squat-pull) and the control group (CG, n = 40). The shoulder girdle and pelvic girdle stability was assessed using the Octobalance Upper Body Test. Results: The GFT increased stability after the intervention and compared to the CG (p = 0.003) as assessed by the relative range of the right (ES: 0.53) and left (ES: 0.57) hemispheres. Besides, most results were within the instrument's error value and the magnitude of the effect was moderate to trivial among the experimental groups. Conclusions: Therefore, ten weeks of functional training performed in a grouped sequence promoted improvements in scapular and lumbar-pelvic girdle stability.

The aim of the study was to compare the EMG amplitude in bench press (stable loads) to bench press using loads moving in anteroposterior and mediolateral directions. Seventeen resistance-trained men, with 9.4±4.7 years of resistance training experience were recruited. After a familiarization session assessing 1 repetition maximum (RM) in the bench press, participants performed: 1) bench press with traditional stable loading 2) bench press with loads (2x5kg) attached as pendulums swinging forward/backwards and 3) left/right in randomized order. The total load was 70% of the 1RM load. Electromyography was measured in the pec-toralis major, anterior-and posterior deltoid, biceps brachii, triceps brachii and external obli-ques. Using stable loads, the pectoralis major demonstrated lower EMG amplitude compared to the two unstable conditions. In the external obliques, the stable conditions demonstrated lower EMG amplitude than the swing in the mediolateral direction, but not the anteroposterior direction. There were no differences between two swinging loads or the three conditions for the triceps brachii, biceps brachii, anterior deltoid or posterior deltoid. In conclusion, swinging in bench press resulted in similar EMG amplitude in the shoulder-and arm muscles, but greater pectoralis and external oblique (only mediolateral swing) activity compared to bench press.

PurposeTo determine the effects of asymmetric loads on muscle activity with the bench press.Method Seventeen resistance-trained men performed one familiarization session including testing one repetition maximum (1RM) and three 5 repetition maximum (RM) lifts; using symmetric loads, 5% asymmetric loads, and 10% asymmetric loads. The asymmetric loading (i.e., reduced load on one side) was calculated as 5% and 10% of the subject`s 1RM load. In the experimental session, the three conditions of 5RM were conducted with electromyographic activity from the pectoralis major, triceps brachii, biceps brachii, anterior deltoid, posterior deltoid, and external oblique on both sides of the body.ResultsOn the loaded side, asymmetric loads reduced triceps brachii activation compared to symmetric loads, whereas the other muscles demonstrated similar muscle activity between the three conditions. On the de-loaded side, 10% asymmetry in loading resulted in lower pectoralis major, anterior deltoid, and biceps brachii activation compared to 5% asymmetric and symmetric loading. On the de-loaded side, only pectoralis major demonstrated lower muscle activation than symmetric loads. Furthermore, asymmetric loads increased external oblique activation on both sides compared to symmetric loads.Conclusions Asymmetric bench press loads reduced chest and shoulder muscle activity on the de-loaded side while maintaining the muscle activity for the loaded side. The authors recommend resistance-trained participants struggling with strength imbalances between sides, or activities require asymmetric force generation (i.e., alpine skiing or martial arts), to implement asymmetric training as a supplement to the traditional resistance training.

Balance as a skill and task-specific capacity is considered an essential physical quality in curling, required for executing effective stone delivery. However, no testing protocols have been developed to test curling-specific balance in the delivery position. Thus, the primary aim of this study was to investigate the reliability , validity and usefulness of a newly-developed, curling-specific balance test (CSBT) which involved the delivery position. The secondary aim was to examine the differences between elite and sub-elite curlers for core strength and flexibility, which have previously been identified as important qualities in curling and determinants of balance. Twenty curling players (13 females aged 19 ± 3.1 years; 7 males aged 19.6 ± 2.3 years) from five Swedish super-league curling clubs were divided into two groups according to playing level: elite and sub-elite. Variables included body mass, body height, body mass index, age, playing experience, training frequency, plank test, sit and reach test, standing single-leg balance test (SLBT) and CSBT. The CSBT was executed on a multiaxial tilting balance plate while mimicking the curling delivery position (i.e., a deep lunge position with the front foot on the plate). The participants completed the CSBT on three separate occasions, with each test consisting of three, 20-s attempts. Both the relative and absolute reliability were good for the CSBT (ICC = 0.90; CV = 14.5%). The CSBT demonstrated good measurement usefulness, being sensitive to detect moderate changes that exceeded 0.5 times the test standard deviation. Construct validity of the CSBT was evidenced by the large discriminatory capacity to differentiate expertise level in curling players (t-test: 2.85, p < 0.01; large ES), irrespective of other physical capacities (e.g., flexibility and core strength). However, the elite and sub-elite players also differed in age, playing experience and training frequency. Content validity was confirmed by a weak correlation (r = 0.21; 95%CI:-0.26 to 0.60) between the CSBT and SLBT, which suggests that curling-specific and standing balance should be considered as independent and task-specific motor skills. In conclusion, the CSBT can be used as a reliable, valid and useful tool for the assessment of curling-specific balance performance. In addition, longer and more extensive involvement in curling training contributed to superior specific balance in elite curlers.

Background: Activities which simultaneously challenge both physical and cognitive function are promising strategies for promoting cognitive function. Objective: To examine the effects of resistance exercise with instability and traditional resistance exercise compared with a health education control on cognitive function in older adults with cognitive complaints. Methods: Sixty-seven participants were randomized to either 12 weeks of thrice-weekly resistance exercise (RE = 23), RE with instability (REI = 22), or a weekly health education control (CON = 22). At each training session, RE and REI participants performed seven exercises for three sets and 10-15 repetitions. REI participants performed each exercise using instability devices. The primary outcome was a composite score of global cognitive function. Secondary outcomes included composite scores for cognitive sub-domains and physical function. Results: Most participants were women (REI: 77%; RE = 78%; CON = 77%; mean age of 71 years), and did not need transport to the intervention site. At completion, compared with CON, REI and RE did not significantly improve on global cognition or each cognitive sub-domain. Both exercise groups improved on the timed up and go (REI - CON: -1.6 s, 95% CI: [-2.6, -0.5]; RE - CON: -1.4 s, 95% CI: [-2.4, -0.5) and 1-RM (REI - CON: 24 kg, 95% CI: [11, 36]; RE - CON: 25 kg, 95% CI: [12, 37]). An exploratory contrast showed that compared with RE, REI promote greater gains on global cognition (2.20, 95% CI: [0.10, 4.31]) and memory (1.34; 95% CI: [0.15, 2.54]). Conclusion: REI did not substantially improve cognitive function but did promote physical function among older adults with cognitive complaints. However, compared with RE, REI improved global cognition and memory.

Instability resistance training (RT) or exercising within an unstable environment is a popular training modality and frequently used in training, rehabilitation and prevention settings. Yet, due to the reported reduced force output during exercising within unstable condition, instability RT is said to lack the necessary overload to induce meaningful effects. However, empirical evidence of interventions suggests otherwise. The aim of this study was to systematically analyse instability RT vs. stable RT and discuss potential mechanisms. Therefore, we analysed squats within more unstable and more stable environments and calculated transversal and vertical forces. Greater transversal plane ground reaction forces were observed while performing squats on the more unstable surface (p ≤ .001; d = 3.70, BF10 = 53213.49). In contrast, vertical force output remained similar for both conditions (p = .058; d = 1.14, BF10 = 1.36).

Research regarding the relationship between core muscle endurance and performance is limited. The purpose of this study was to analyze the association between core/trunk endurance and athletic performance. Seventy-four healthy participants between 18 and 45 years old participated in this study (Age: 26.0 ± 6.5 years; Mass: 74.6 ± 12.8 kg; Height: 1.74 ± 0.08 m; BMI: 19.0 ± 6.8 kg/m2). The core endurance was measured using the McGill protocol, consisting of the following tests: trunk flexion, back extension, and side-bridge. Functional performance was evaluated with push-ups, sit to stand, T-run test, countermovement jump (CMJ), Yo-Yo test, maximum dynamic strength-one repetition maximum (1RM) and muscle power on the bench press, pull row, and leg press. The regression results between the McGill protocol (proxy for core/trunk endurance) and the dependent variables were: 1RM pull row: r2 = 0.109 with p = 0.046; RM bench press: r2 = 0.149 with p = 0.012; RM leg press: r2 = 0.144 with p = 0.013 and power pull row: r2 = 0.151 with p = 0.016; power bench press: r2 = 0.136 with p = 0.026; power leg press: r2 = 0.122 with p = 0.013), push-ups: r2 = 0.157 with p < 0.001, sit to stand: r2 = 0.198 with p < 0,001), functional movement score: r2 = 0.209 with p < 0.001). Nevertheless, core endurance scores were not able to predict jump ability (r2 = 0.014, p = 0.807) or agility (T-test: 0.036 with p = 0.497). In conclusion, core endurance exerted no significant influence the agility and jump performance but influenced the ability to run intermittently, exert maximum power and strength in different actions (push, pull, and lift exercises) related to the better quality of movement (FMS).

Objective: To evaluate the effects of 24-weeks of strength training on stable (ST) and unstable surfaces (UST) on the functional mobility, balance and concern about falling in healthy older adults, younger than 70. Design: A single-center, randomized clinical trial. Participants: Sixty-four older adults (58 females and 6 males; 68 years) were randomized into control, ST or UST groups. Interventions: Both ST and UST intervention groups received a core muscles, upper and lower limbs, moderate-intensity strength exercises using stable and unstable surfaces. The classes were performed three times per week over a 24-week period. The control group did not receive any type of active intervention. Measurements: The primary outcomes measure were the dynamic balance (Berg Balance Scale (BBS)) and functional mobility (timed up and go test (TUG)). The secondary outcomes included the sitting and rising test (SRT) and Falls Efficacy Scale International (FESI) scores. Results: There was a significant improvement in balance performance (BBS= +4 points) after 24-weeks of both ST (+1.22; 95% CI- .19 to 2.63) and UST (+2.26; 95% CI, .83 to 3.70) compared with the control group. Additionally, compared with the control, only UST experienced functional mobility gains (TUG= -2.44; 95% CI, -4.41 to - .48; SRT= +1.12; 95% CI, .08 to 2.17) and decreased concern about falling (FESI= -4.41; 95% CI, -9.30 to -.27). Conclusion: Long-term ST with and without unstable devices were effective to improve dynamic balance in older adults. Furthermore, the effects of UST were extended to functional mobility gains, and reduced concern about falling. This article is protected by copyright. All rights reserved.

The aim of this study was to assess the short-and long-term effects of resistance training (RT) with different stability requirements. Fifty-nine men underwent a 3-week familiarization period followed by a 7-week training period. During familiarization, all participants trained four sessions of squats with a Smith machine, free weights and free weights standing on a wobble board. After week-3, participants were randomized into a low (Smith machine), medium (Free-weight) or high (Wobble board) stability RT program, and Control group. All participants were tested pre-, after week-3 and post-intervention. Ten repetition maximum (10RM), rate of force development (RFD), electromyography (EMG) and maximum voluntary isometric contraction (MVIC) were tested in all three squat conditions in addition to countermovement jump (CMJ) on stable and unstable surfaces, and muscle thickness. After familiarization, greater 10RM loads (21.8-27.3%), MVIC (7.4-13.5%), RFD (29.7-43.8%) and CMJ (4.9-8.5%) were observed in all conditions. Between week 3 and 10, the Free-weight and Wobble board groups similarly improved 10RM in all conditions. Smith machine group demonstrated greater improvement in the trained exercise than the medium and high stability exercises. All training groups showed similar improvement in muscle thickness , RFD and MVIC. There was no CMJ improvement on the stable surface, but the Wobble board group demonstrated significantly greater improvement on the unstable surface. In conclusion, low, medium or high stability RT resulted in similar improvements in trained and non-trained testing conditions except for greater CMJ on the unstable surface in the Wobble group. Greater 10RM strength in trained than non-trained exercise was only observed in low stability group. Familiarization was associated with substantial improvements in 10RM and CMJ, with greater improvement associated with higher stability requirements. These findings suggest that high stability can increase strength, muscle thickness and explosive measurements similar to training with lower stability.

Effect of instability resistance training on cognitive function in the elderly.

Ten resistance trained (RT) and 6 non-resistance trained (NRT) subjects were used to determine differences in quadriceps activation between isometric single and double knee extensions and squat contractions. Greater inactivation, as measured by the interpolated twitch technique, was recorded with single (RT: 16.5%, NRT: 17.6%) than double leg extensions (RT: 8.4%, NRT: 13.4%) or squats (RT: 4.03%, NRT: 1.7%). There was no significant difference between the maximum voluntary contraction (MVC) force of the dominant leg during single and double leg extensions. However, in NRT subjects, the contralateral or non-dominant leg during double leg extensions exhibited significantly less force than the dominant leg (715.9 vs 566.9 N). This deficit may be due to a lesser reliance on the non-dominant limb. The contractions of multiple lower body muscle groups enhanced the activation of the dominant quadriceps. Greater levels of activation may be necessary to cope with the stabilization necessary for bilateral and multi-articular contractions.

The aim of the study was to compare muscle activity using the same relative resistance in squats and Bulgarian squats on stable and unstable surface. Muscle strength and activity were assessed by 6-repetition maximum and concomitant surface electromyography. A cohort of 15 resistance-trained males performed the exercises on the floor or a foam cushion in randomized order. The muscle activity was greater in biceps femoris (63-77%, p<0.01) and core muscle external obliques (58-62%, p<0.05) for the Bulgarian squat compared to regular squats, but lower for rectus femoris (16-21%, p<0.05). Only Bulgarian squat showed differences concerning the surface, e. g. the unstable surface reduced the activation of erector spinae (10%, p<0.05) and biceps femoris (10%, p<0.05) compared to a stable surface. There were similar activations in the vasti muscles and rectus abdominis between the different exercises (p=0.313-0.995). Unstable surfaces resulted in a load decrement of 7% and 10% compared to stable surfaces (p<0.001). In conclusion, the squat was somewhat favorable for the activation of agonists, whereas Bulgarian squat was advantageous for the antagonist and somewhat for core muscles. Bulgarian- and regular squats complement each other, and it may be useful to include both in a periodized resistance training program.

The purpose of this study was to compare one-repetition maximum (1-RM) and muscle activity in three chest-press exercises with different stability requirements (Smith machine, barbell, and dumbbells). Twelve healthy, resistance-trained males (age 22.7 ± 1.7 years, body mass 78.6 ± 7.6 kg, stature 1.80 ± 0.06 m) were tested for 1-RM of the three chest-press exercises in counterbalanced order with 3-5 days of rest between the exercises. One-repetition maximum and electromyographic activity of the pectoralis major, deltoid anterior, biceps, and triceps brachii were recorded in the exercises. The dumbbell load was 14% less than that for the Smith machine (P ≤ 0.001, effect size [ES] = 1.05) and 17% less than that for the barbell (P ≤ 0.001, ES = 1.11). The barbell load was ∼3% higher than that for the Smith machine (P = 0.016, ES = 0.18). Electrical activity in the pectoralis major and anterior deltoid did not differ during the lifts. Electrical activity in the biceps brachii increased with stability requirements (i.e. Smith machine <barbell <dumbbells; P ≤ 0.005; ES = 0.57, 1.46, and 2.00, respectively), while triceps brachii activity was reduced using dumbbells versus barbell (P = 0.007, ES = 0.73) and dumbbells versus Smith machine (P = 0.003, ES = 0.62). In conclusion, high stability requirements in the chest press (dumbbells) result in similar (pectoralis major and anterior deltoid), lower (triceps brachii) or higher (biceps brachii) muscle activity. These findings have implications for athletic training and rehabilitation.

Little is known about the effect of performing upper-body resistance exercises with dumbbells versus barbells and standing versus seated. Therefore, this study sought to compare electromyogram activity (EMG) and one-repetition maximum (1-RM) in barbell and dumbbell shoulder presses performed seated and standing. 15 healthy men volunteered for 1-RM and EMG testing with a load corresponding to 80% of the 1-RM. EMG was measured in the anterior, medial and posterior deltoids, and biceps and triceps brachii. The following EMG differences or trends were observed: For deltoid anterior: ∼11% lower for seated barbell versus dumbbell (P=0.038), ∼15% lower in standing barbell versus dumbbell (P<0.001), ∼8% lower for seated versus standing dumbbells (P=0.070); For medial deltoid, ∼7% lower for standing barbell versus dumbbells (P=0.050), ∼7% lower for seated versus standing barbell (P=0.062), 15% lower for seated versus standing dumbbell (P=0.008); For posterior deltoid: ∼25% lower for seated versus standing barbell (P<0.001), ∼24% lower for seated versus standing dumbbells (P=0.002); For biceps, ∼33% greater for seated barbell versus dumbbells (P=0.002), 16% greater for standing barbell versus dumbbell (P=0.074), ∼23% lower for seated versus standing dumbbells (P<0.001); For triceps, ∼39% greater for standing barbell versus dumbbells (P<0.001), ∼20% lower for seated versus standing barbell (P=0.094). 1-RM strength for standing dumbbells was ∼7% lower than standing barbell (P=0.002) and ∼10% lower than seated dumbbells (P<0.001). In conclusion, the exercise with the greatest stability requirement (standing and dumbbells) demonstrated the highest neuromuscular activity of the deltoid muscles, although this was the exercise with the lowest 1-RM strength.