Squat Force Research Articles

Dynamic Strength Index in Basketball Players: Age and Position Differences, Seasonal Variation and Association with Sprinting and Change of Direction Performance

AbstractThe aim of the study was to investigate the differences in bilateral and unilateral dynamic strength index (DSI) between age categories (seniors and juniors), player positions (guards and forwards), its variation during the basketball season, and its association with sprint and change of direction (CoD) performance. Highly trained basketball players (n = 32) performed bilateral and unilateral countermovement jumps (CMJ), bilateral and unilateral isometric squats, 10-m sprint, and 505 CoD test. DSI was calculated from CMJ and isometric peak force, while 10-m sprint and 505 test were used to calculate the CoD deficit. Two-way factorial analysis showed larger isometric peak force in seniors, and larger bilateral DSI in juniors, while guards had higher DSI values and larger peak force in both metrics compared to forwards. Two-way mixed model ANOVA showed a significant increase in unilateral isometric squat and CMJ peak force force (g = –0.08 to –0.64) and increase in bilateral DSI values. Post-hoc analysis showed that isometric squat force significantly increased only in seniors (g = 0.88), resulting in decreased bilateral DSI values (g = 0.52), with bilateral and unilateral DSI values increasing in juniors. Similar trends were observed in guards and forwards, with guards exhibiting a more pronounced increase in all variables compared to forwards. Furthermore, correlation analysis for in-season testing showed moderate associations between isometric squat peak force and CoD ability (r = –0.43 to –0.54; P < 0.001), and weak associations between DSI and CoD ability (r = 0.36 to 0.39; P < 0.05), while associations were not significant for sprint performance. The relationships were lower or absent during pre-season testing. Further interventional studies are needed to determine the usefulness of DSI to guide training related decision-making.

Neuromechanical Consequences of Eccentric Load Reduction During the Performance of Weighted Jump Squats.

To quantify the acute effects of a spectrum of eccentric load reductions on neuromechanical adjustments during the performance of weighted jump squats (WJSs). On separate days, 16 well-trained participants performed WJS trials with various eccentric load reductions (0% [body mass only], 25%, 50%, 75%, and 100% [standard WJS] of concentric load) with a mechanical braking unit, while concentric load was set at 30% of peak isometric squat force in all trials. A force platform and a motion-capture system were used to assess neuromuscular performance. Peak power output was 6.2% (4.7%) higher when load was reduced by 50% versus 0% (55.4 [7.8] vs 51.9 [7.6]W/kg; P = .001). Compared with no braking (0.326 [0.059]m), jump height was ∼13% to 17% higher for all eccentric load reduction conditions (all P < .001). Vertical ground reaction forces were progressively lower for 25%, 50%, 75%, and 100% loading conditions (-22.1% [14.6%], -32.3% [10.8%], -42.0% [13.2%], and -46.1% [14.7%]; all P ≤ .001) in reference to body mass only. Eccentric load reduction is advantageous compared with traditional isoinertial loading for improving both jump height and peak power output during the concentric portion of maximal-effort WJS. This practice also decreases mechanical constraints in the lower extremities, which may become beneficial for load-compromised individuals.

Stable vs. variable eccentric load. Do they induce different training and physical performance outcomes?

ABSTRACT Since most movements on the field require athletes to produce forces in variable and unpredictable contexts, the use of training programs based on identical repetitions of an exercise may not be optimal for movement transference. Therefore, the aim of this study was to analyse the effects of unexpected eccentric load variability during resistance training in team sport players. Sixty-three men were randomly allocated to two experimental groups (Variable (VTG) and stable (STG) training group) and control group: (CG) volunteered to participate in this study. Experimental groups trained with the same average load of half-squat exercise twice a week for six weeks using rotary inertial devices (RIDs) with (VTG) and without (STG) an unexpected variability of the load. The squat force was measured for every session with force plates. Counter-movement jump (CMJ), sprint, and change of direction performances were measured pre and post-test. CMJ performance improved for VTG (p = .014; ES = 0.7) and STG (p = .005; ES = 0.79) but not for CG. Exposure to high eccentric forces with RIDs lead athletes to improve physical performance in the trained force vector but, since RIDs induce in high levels of variability per se, increasing the level of variability of the exercise will not add benefits to physical performance and training outcomes. HIGHLIGHTS The relevance of the study is to analyse if increasing the variability of the load will improve the athlete output to different physical performance tests. The exposure to eccentric overload with RIDs during the squat exercise allows to greater CMJ height improvements than those seen in the literature with RIDs without overloading the eccentric contraction. RIDs induce in high level of variability per se. Therefore, increasing the level of variability of the exercise will not add benefits to physical performance and training outcomes.

Determining concentric and eccentric force\u2013velocity profiles during squatting

PurposeThe force–velocity relationship of muscular contraction has been extensively studied. However, previous research has focussed either on isolated muscle or single-joint movements, whereas human movement consists of multi-joint movements (e.g. squatting). Therefore, the purpose of this study was to investigate the force–velocity relationship of isovelocity squatting.MethodsFifteen male participants (24 ± 2 years, 79.8 ± 9.1 kg, 177.5 ± 6 cm) performed isovelocity squats on a novel motorised isovelocity device (Kineo Training System) at three concentric (0.25, 0.5, and 0.75 m s−1) and three eccentric velocities (− 0.25, − 0.5, and − 0.75 m s−1). Peak vertical ground reaction forces, that occurred during the isovelocity phase, were collected using dual force plates (2000 Hz) (Kistler, Switzerland).ResultsThe group mean squat force–velocity profile conformed to the typical in vivo profile, with peak vertical ground reaction forces during eccentric squatting being 9.5 ± 19% greater than isometric (P = 0.037), and occurring between − 0.5 and − 0.75 m s−1. However, large inter-participant variability was identified (0.84–1.62 × isometric force), with some participants being unable to produce eccentric forces greater than isometric. Sub-group analyses could not identify differences between individuals who could/could not produce eccentric forces above isometric, although those who could not tended to be taller.ConclusionsThese finding suggest that variability exists between participants in the ability to generate maximum eccentric forces during squatting, and the magnitude of eccentric increase above isometric cannot be predicted solely based on a concentric assessment. Therefore, an assessment of eccentric capabilities may be required prior to prescribing eccentric-specific resistance training.

Relationships between Muscle Architecture and Performance in Division I Male Italian Field Hockey Players

Muscle architecture has been proposed as one of the most important determinants of muscle strength and power performance. The purpose of the present investigation was to correlate the muscle architecture with power, agility and maximal strength in Italian division I Field Hockey (FH) players. Twenty players (age = 25.4 ± 5.2 y; body mass = 78.5 ± 9.0 kg; body height = 179.6 ± 7.8 cm) were assessed for body composition, agility, sprint and maximal isometric force in squat (ISQ). The pro-agility test (PRO) and 30-m sprint (SPRINT) were used for agility and speed assessments, respectively. In addition, the pennation angle (PA), fascicle length (FL) and muscle thickness (MT) of the vastus lateralis were assessed via B-mode ultrasound. Large positive correlations were found between PRO and both PA and MT (r = 0.62; p = 0.006 and r = 0.51; p = 0.032, respectively). Moreover, SPRINT was positively correlated with PA and negatively correlated with FL (r = 0.50, p = 0.046; and r = −0.50; p = 0.034, respectively). Large positive correlations were also detected between body fat and both PRO and SPRINT (r = 0.58; p = 0.012 and r = 0.61; p = 0.009, respectively), indicating detrimental effects of the body fat on specific performances. The present findings showed the existence of large relationships between the muscle architecture of the vastus lateralis and physical characteristics related to elite performance in FH. Low PA and long FL of the vastus lateralis appear important parameters for agility and sprint performances.

Early Functional and Morphological Muscle Adaptations During Short-Term Inertial-Squat Training.

Purpose: To assess early changes in muscle function and hypertrophy, measured as increases in muscle cross-sectional areas (CSAs) and total volume, over a 4 weeks inertial resistance training (RT) program.Methods: Ten young RT-naive volunteers (age 23.4 ± 4.1 years) underwent 10 training sessions (2–3 per week) consisting of five sets of 10 flywheel squats (moment of inertia 900 kg⋅cm2). Magnetic resonance imaging (MRI) scans of both thighs were performed before (PRE), and after 2 (IN) and 4 (POST) weeks of training to compute individual muscle volumes and regional CSAs. Scans were performed after ≥96 h of recovery after training sessions, to avoid any influence of acute muscle swelling. PRE and POST regional muscle activation was assessed using muscle functional MRI (mfMRI) scans. Concentric (CON) and eccentric (ECC) squat force and power, as well as maximal voluntary isometric contraction force (MVIC) of knee extensors and flexors, were measured in every training session.Results: Significant quadriceps hypertrophy was detected during (IN: 5.5% ± 1.9%) and after (POST: 8.6% ± 3.6%) the training program. Increases in squat force (CON: 32% ± 15%, ECC: 31 ± 15%) and power (CON: 51% ± 30%, ECC: 48% ± 27%) were observed over the training program. Knee extensor MVIC significantly increased 28% ± 17% after training, but no changes were seen in knee flexor MVIC. No correlation was found between regional muscular activation in the first session and the % of increase in regional CSAs (r = -0.043, P = 0.164).Conclusion: This study reports the earliest onset of whole-muscle hypertrophy documented to date. The process initiates early and continues in response to RT, contributing to initial increases in force. The results call into question the reliability of mfMRI as a tool for predicting the potential hypertrophic effects of a given strengthening exercise.

FORCE-VELOCITY RELATIONSHIP OF LEG EXTENSORS OBTAINED FROM THREE DIFFERENT TYPES OF LOAD

The first aim of this study was to evaluate the shape of force-velocity (F-V) relationships in case of gravitational (W), inertial (I) and combined (W+I) type of load assessed from squat jump (SJ) performed on a modified Smith machine. The second aim was to determine whether there were differences between the same parameters (maximal force, F0; maximal velocity, V0; maximal power, P0) obtained from linear F-V relationship among three different loads. The third aim was to evaluate the concurrent validity of the parameters F0 obtained from different types of load in SJ, with maximum isometric force in squat (Fiso), as well as one repetition maximum in squat (1RM). Fifteen male participants were tested in SJ with three different types of load, squat for obtaining 1RM and isometric squat for obtaining the Fiso. The observed F-V relationships were exceptionally strong and approximately linear (median r ≥ 0.98) independently of used load. The differences between same parameters of different types of load were determined in parameters F0 and V0, while there were no differences between P0. Regarding third aim, concurrent validity for F0 showed to be moderate to high and significant in all 3 types of load (r ≥ 0.56), except between F0 and Fiso in W type of load, where it was non-significant (r ≥ 0.47). The significance of the study reflects in better understanding of the mechanisms of the functioning of muscle system in case of different types of load. Future studies should investigate the impact of different types of load to kinetic and kinematic parameters in case of different motoric tasks and muscle groups.

Strength and Power Qualities Are Highly Associated With Punching Impact in Elite Amateur Boxers.

This study investigated the relationship between punching impact and selected strength and power variables in 15 amateur boxers from the Brazilian National Team (9 men and 6 women). Punching impact was assessed in the following conditions: 3 jabs starting from the standardized position, 3 crosses starting from the standardized position, 3 jabs starting from a self-selected position, and 3 crosses starting from a self-selected position. For punching tests, a force platform (1.02 × 0.76 m) covered by a body shield was mounted on the wall at a height of 1 m, perpendicular to the floor. The selected strength and power variables were vertical jump height (in squat jump and countermovement jump), mean propulsive power in the jump squat, bench press (BP), and bench throw, maximum isometric force in squat and BP, and rate of force development in the squat and BP. Sex and position main effects were observed, with higher impact for males compared with females (p ≤ 0.05) and the self-selected distance resulting in higher impact in the jab technique compared with the fixed distance (p ≤ 0.05). Finally, the correlations between strength/power variables and punching impact indices ranged between 0.67 and 0.85. Because of the strong associations between punching impact and strength/power variables (e.g., lower limb muscle power), this study provides important information for coaches to specifically design better training strategies to improve punching impact.

Effects of long term supplementation of anabolic androgen steroids on human skeletal muscle.

The effects of long-term (over several years) anabolic androgen steroids (AAS) administration on human skeletal muscle are still unclear. In this study, seventeen strength training athletes were recruited and individually interviewed regarding self-administration of banned substances. Ten subjects admitted having taken AAS or AAS derivatives for the past 5 to 15 years (Doped) and the dosage and type of banned substances were recorded. The remaining seven subjects testified to having never used any banned substances (Clean). For all subjects, maximal muscle strength and body composition were tested, and biopsies from the vastus lateralis muscle were obtained. Using histochemistry and immunohistochemistry (IHC), muscle biopsies were evaluated for morphology including fiber type composition, fiber size, capillary variables and myonuclei. Compared with the Clean athletes, the Doped athletes had significantly higher lean leg mass, capillary per fibre and myonuclei per fiber. In contrast, the Doped athletes had significantly lower absolute value in maximal squat force and relative values in maximal squat force (relative to lean body mass, to lean leg mass and to muscle fiber area). Using multivariate statistics, an orthogonal projection of latent structure discriminant analysis (OPLS-DA) model was established, in which the maximal squat force relative to muscle mass and the maximal squat force relative to fiber area, together with capillary density and nuclei density were the most important variables for separating Doped from the Clean athletes (regression = 0.93 and prediction = 0.92, p<0.0001). In Doped athletes, AAS dose-dependent increases were observed in lean body mass, muscle fiber area, capillary density and myonuclei density. In conclusion, long term AAS supplementation led to increases in lean leg mass, muscle fiber size and a parallel improvement in muscle strength, and all were dose-dependent. Administration of AAS may induce sustained morphological changes in human skeletal muscle, leading to physical performance enhancement.

Electromyographic Amplitude vs. Concentric and Eccentric Squat Force Relationships for Monoarticular and Biarticular Thigh Muscles

This study examined the linearity of the electromyographic (EMG) amplitude vs. concentric and eccentric squat force relationships for monoarticular and biarticular thigh muscles. Fourteen resistance-trained men (mean age ± SD: 22 ± 2 years; estimated thigh muscle cross-sectional area: 221.9 ± 22.7 cm) performed concentric and eccentric squats using a novel testing device from 10 to 90% of their maximum average force. Surface EMG signals were detected from the right vastus lateralis, rectus femoris, and biceps femoris. Linear regression was used to examine the relationships between EMG amplitude and force, and repeated measures analyses of variance were used to assess differences among the muscles. Moderate-to-high coefficients of determination were found for the vastus lateralis for both concentric and eccentric testings (r = 0.587-0.992). For the biceps femoris, the mean linear slope coefficient was significantly greater for concentric vs. eccentric testing (0.044 vs. 0.013 μV RMS·N; p = 0.002; effect size = 1.44). Although EMG amplitude for the vastus lateralis and rectus femoris increased with changes in eccentric force output, the electrical activity of the biceps femoris remained stable. These results demonstrated that the EMG amplitude vs. force relationships for the vastus lateralis were linear, despite the fact that force production during the squat is related to the activation of muscles that must simultaneously function as agonists and antagonists. Our findings for eccentric force testing are in agreement with investigations showing reduced hip extensor activity during concurrent extension at the hip and knee joints.

Seasonal changes in leg strength and vertical jump ability in internationally competing ski jumpers

The aim of the present study was to investigate the effects of the seasonal changes in heavy strength training on maximal strength and vertical jump ability in internationally competing ski jumpers. A repeated-measures design was used to follow-up the changes in strength, vertical jump capacity, and neuromuscular efficiency (expressed as the ratio between squat jump height and the relative isometric force) in the ski jumpers. Measurements were performed in November (pre), January (middle of the competition season), and in March (end of the competition season). The weekly number of strength training sessions, absolute, and relative peak isometric squat force was significantly reduced during the competition period (p < 0.05). The body mass was reduced from pre-season to the middle of the competition season and remained at this level at the end of the competition season (p < 0.05). Squat jump height remained unchanged from pre-season until the end of the competition season (p < 0.05). Neuromuscular efficiency increased from pre-season until the end of the competition season (p < 0.05). The present study shows that maximal strength and body weight is reduced from pre-season to the end of the competitive season in internationally competing ski jumpers. The vertical jump ability did not change from pre-season to the end of the competitive season, while the neuromuscular efficiency increased during the competitive season. These findings indicate that coaches and athletes should emphasize adequate nutritional strategies and to apply a larger focus on strength maintenance training during the competitive season to maximize ski jump performance.

Recovery Patterns in Electroencephalographic Global Field Power During Maximal Isometric Force Production

In previous work, cortical activity decreased with fatigue following novel movements or small muscle group actions. These muscle actions, however, do not appear related to the cortical activity seen with biologically relevant and highly trained movement patterns (i.e., ingrained patterns). The cortical recovery response to ingrained patterns-and how it differs with altered load, speed, or volume - is unknown. The purpose of this balanced, within-group study was to investigate differences in cortical activity 24 hours after physically distinct variations of a highly trained squat exercise (n = 7, minimum 4 years resistance training experience). Four resistance protocols were chosen: rate of force development (PWR, 6 × 3 squat jumps at 30% of 1 repetition maximum [1RM]); magnitude of force development (FOR, 6 × 3 squat at 95% of 1RM); volume of force development (VOL, 6 × 10 squat at 80% of their 1RM); and control (CTRL, 6 sets unracking an empty bar). Twenty-four hours later, subjects performed a peak isometric squat while electroencephalographic and biochemical markers of exertion and fatigue were obtained. Global field power detected the quantity of activity superficial to motor regions. Waveforms of activity throughout the isometric squats were obtained and grand averages calculated to produce quantitative depictions of cortical activity. Significance was P ≤ 0.05. Peak isometric squat force was not statistically different 24 hours postexercise (Force [N]: PWR: 2828.79 ± 461.17; FOR: 2887.64 ± 453.09; VOL: 2910.17 ± 625.81; CTRL 2768.53 ± 374.85). Subjects produced similar and characteristic cortical activity patterns during isometric squats despite varying indices of fatigue. Differences were observed based upon the use or nonuse of aerobic endurance exercise in their training program. Patterns of activity in data seem to have emerged based on differences in training preference. Global Field Power (uV) during the isometric squat for PWR was 26.98 ± 14.64; FOR 24.06 ± 19.05; VOL 23.05 ± 13.37; and CTRL 15.78 ± 8.11. Previous research suggests that cortical activity decreases with physical activity; however, despite substantial endocrine, perceptual, and biomechanical differences between protocols, cortical activity was not decreased below control during the performance of a maximal isometric squat 24 hours after various exercise protocols.

Does Cluster Loading Enhance Lower Body Power Development in Preseason Preparation of Elite Rugby Union Players?

The purpose of this study was to ascertain whether cluster training led to improved power training adaptations in the preseason preparation of elite level rugby union players. Eighteen highly trained athletes were divided into 2 training groups, a traditional training (TT, N = 9) group and a cluster training (CT, N = 9) group before undertaking 8 weeks of lower body resistance training. Force-velocity-power profiling in the jump squat movement was undertaken, and maximum strength was assessed in the back squat before and after the training intervention. Two-way analysis of variance and magnitude-based inferences were used to assess changes in maximum strength and force, velocity, and power values pretraining to posttraining. Both TT and CT groups significantly (p < 0.05) increased maximum strength posttraining. There was a possibly negative effect for the CT group on maximum strength when compared with that for the TT group (pretraining to posttraining change = 14.6 ± 18.0 and 18.3 ± 10.1%, respectively). There were no significant differences pretraining to posttraining for any jump squat force, velocity, or power measures. However, magnitude-based inferences showed that there was a likely positive effect of CT when compared with that of TT for peak power (pretraining to posttraining change = 7.5 ± 7.0 and 1.0 ± 6.2%, respectively) and peak velocity at 40 kg (pretraining to posttraining change = 4.7 ± 6.1 and 0.0 ± 5.0%, respectively) and for peak velocity at body weight (pretraining to posttraining change = 3.8 ± 3.4 and 0.5 ± 3.8%, respectively). Although both a traditional and cluster training loading pattern improved lower body maximum strength in a highly trained population, the traditional training structure resulted in greater maximum strength adaptation. There was some evidence to support the possible benefit of cluster type loading in training prescription for lower body power development.

EEG Measures of Cortical Activity Return to Baseline Within 24 Hours Despite Differential Protocols Emphasizing Force, Power, and Volume

PURPOSE: While a clearer image of the physiological process of recovery from physical exertion is emerging, research into the recovery of the central nervous system is still in its infancy. The purpose of this study was to investigate the nature of motor cortical activity and peak force production 24 hours after resistance exercise. METHODS: Four resistance training protocols were chosen based on their differential interaction with force production: high power (6 x 3 squat jumps at 30% of 1RM); high force (6 x 3 squat at 95% of 1RM); high volume (6 x 10 at 80% of their 1RM); and a control day (6 sets of unracking an empty bar). Twenty-four hours after the intervention, subjects returned to perform a peak isometric squat along with corresponding EEG, perceptual, and blood measures. To control for the rate of adaptation, only highly trained male subjects (years of training: 6+/−1 yrs; squat 1RM: 174+/−26 kg; age: 22+/−3 yrs; body mass: 84.76+/−9.86 kg; n = 7) were included in this study. Cortical activity was measured using an Ag-AgCl electrode-cap, a 40-channel monopolar digital amplifier, and an expanded International 10–20 electrode placement. Linked-ears reference, a ground scalp electrode, and eye electrodes were used to account for electrical artifacts (facial contractions). Movement artifacts were removed using a spatial filter. A 32-bit analog-to-digital converter was used to digitize signals at a sampling rate of 1000hz. High and low frequency bandpass was set at DC and 100hz respectively and signals were low-pass filtered at 50hz using an Infinite Impulse Response (IIR) recursive filter set to a roll-off of 12dB/oct. Impedance was maintained at or below 5 Kohms throughout the experimental protocol. Channels possessing gross artifacts were eliminated. DC drift was removed using a 3rd order polynomial trend correction for each channel. Epochs were set from the completion of the previous movement or the movement of the bar off the rack to the completion of the next repetition. Pearson product-moment correlation coefficients were determined for selected pair wise variables. One-way and univariate analyses of variance (ANOVA) with repeated measures and Fisher's LSD post-hocs were used to detect significant mean differences. Significance level in this study was set at a 0.05 alpha level. RESULTS: Peak isometric squat force was equated by 24 hours post-exercise. The grand average movement related cortical potential area under the curve and mean global field power amplitude were also equated between recovery protocols. Despite the differences between each protocol, we were unable to detect statistically significant differences (in either mean amplitude or area under the curve) for global field power during isometric squats at an alpha level of 0.05. Therefore, the primary finding of this investigation was that 24 hours after differing maximal exertion force production protocols, cortical activity and peak force appear to recover to baseline. CONCLUSIONS: In the present study, the cortical findings suggest that the central responses of well-trained men recover from differing domains of resistance exercise within twenty-four hours. Practical Applications: It is possible that the central nervous system recovers quickly from resistance exercise in the well-trained population. Other limitations to physiological recovery, such as performance decrement, soreness, or fatigue, may be attributable to peripheral, rather than central, causes. Primary damage, particularly with eccentric movement, cannot be ignored. In addition, our laboratory has shown that exercise-induced hypoxia results in secondary damage to muscle through a series of biochemical reactions. The role of the central nervous system in the control of physiological function cannot be underestimated, and this study should be placed appropriately within the context of this evolving area of research.

Ergogenic effects of betaine supplementation on strength and power performance

BackgroundWe investigated the ergogenic effects of betaine (B) supplementation on strength and power performance.MethodsTwelve men (mean ± SD age, 21 ± 3 yr; mass, 79.1 ± 10.7 kg) with a minimum of 3 months resistance training completed two 14-day experimental trials separated by a 14-day washout period, in a balanced, randomized, double-blind, repeated measures, crossover design. Prior to and following 14 days of twice daily B or placebo (P) supplementation, subjects completed two consecutive days (D1 and D2) of a standardized high intensity strength/power resistance exercise challenge (REC). Performance included bench, squat, and jump tests.ResultsFollowing 14-days of B supplementation, D1 and D2 bench throw power (1779 ± 90 and 1788 ± 34 W, respectively) and isometric bench press force (2922 ± 297 and 2503 ± 28 N, respectively) were increased (p < 0.05) during REC compared to pre-supplementation values (1534 ± 30 and 1498 ± 29 W, respectively; 2345 ± 64 and 2423 ± 84 N, respectively) and corresponding P values (1374 ± 128 and 1523 ± 39 W; 2175 ± 92 and 2128 ± 56 N, respectively). Compared to pre-supplementation, vertical jump power and isometric squat force increased (p < 0.05) on D1 and D2 following B supplementation. However, there were no differences in jump squat power or the number of bench press or squat repetitions.ConclusionB supplementation increased power, force and maintenance of these measures in selected performance measures, and these were more apparent in the smaller upper-body muscle groups.

The Effects of Betaine Supplementation on Strength and Power Performance

Betaine (B) is an organic osmolyte and methyl donor. Organic osmolytes are important for fluid balance during osmotic stress and metabolic methylation reactions. Both are important during resistance exercise given the flux of substrates through metabolic pathways and may benefit strength and power performance. PURPOSE: To determine the efficacy of B supplementation in improving strength and power performance. METHODS: Twelve men (mean ± SD age, 21 ± 3 yr; mass, 79.1 ± 10.7 kg) with a minimum of 3 months resistance training, including the squat exercise, completed two 14-day trials in a balanced, randomized, double-blind, repeated measures, crossover design. Prior to and following 14 days of B supplementation (1.25 g mixed in 240 ml Gatorade®) or placebo (P), consumed twice per day, subjects completed two consecutive days (D1 and D2) of a standardized high intensity/power resistance exercise challenge (REC). A 14-day washout period separated the 14-day B and P trials. Two standardized resistance training workouts were completed during B and P trials, and during the washout period, to maintain the subject's training status. Total body water was measured via multi-frequency bio-electrical impedance spectroscopy. ANOVA were conducted with alpha set at 0.05. RESULTS: Body mass and total body water values did not change over the course of the study. Following 14-days of B supplementation, bench throw power (1779 ± 90 W) and isometric bench press force (2922 ± 297 N) increased (p<0.05) during REC compared to pre-supplementation values and corresponding P values (1535 ± 81 W, 2345 ± 146 N, respectively). Compared to pre-supplementation, vertical jump power and isometric squat force increased (p<0.05) on both D1 and D2. There were no differences in bench press repetitions, number of squat repetitions, and jump squat power between D1 and D2, or between B and P values. CONCLUSION: B supplementation increased power, force and maintenance, particularly in the smaller upper-body muscle groups compared to larger lower-body muscle groups. Funded by Danisco USA Incorporated, Ardsley, NY.

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.

Muscle Fiber Characteristics of Competitive Power Lifters

To examine the skeletal muscle characteristics of power lifters, 5 competitive power lifters (PL; X ± SE; age 5 31.0 ± 1.5 years, squat 5 287.7 ± 15.7 kg, bench press 5 170.5 ± 17.7 kg, and deadlift 5 284.2 ± 7.5 kg) and 5 untrained control subjects (CON; age = 27.3 ± 3.3 years) served as subjects. Iso-kinetic squat force and power was greater (p < 0.05) for the PL at all bar velocities (0.20, 0.82, and 1.43 m · s1), as was vertical jump height and estimated power. Muscle biopsies from the vastus lateralis m. revealed significant differences for percent fiber type (PL, IIA 5 45.5 ± 1.6%, IIB 5 1.3 ± 0.8%; CON, IIA 5 33.4 ± 3.1%, IIB 5 12.0 ± 2.4%); percent fiber type area (PL, IIA 5 51.8 ± 1.6%, IIB 5 1.3 ± 0.8%; CON, IIA 5 43.5 ± 3.4%, IIB 5 12.4 ± 2.6%); and percent myosin heavy chain isoform (PL, IIa 5 59.5 ± 6.1%; CON, 46.5 ± 2.5%). Muscle fiber characteristics were significantly correlated (r = 6 0.61) with numerous strength and power measures for the PL. These data illustrate the muscle fiber characteristics necessary for the maximal force production requirements of power lifting.