Individual Muscle Force Differences During Loaded Hexbar Jumps: A Statistical Parametric Mapping Analysis.

Knowledge of individual muscle force during strength and conditioning exercises provides deeper understanding of how specific training decisions relate to desired training outcomes. The purpose of this study was to estimate individual muscle forces during hexbar jumps with 0%, 20%, 40%, and 60% of the hexbar deadlift 1-repetition maximum utilizing in vivo motion capture and computational modeling techniques of male participants. Muscle forces for the gluteus maximus, biceps femoris, rectus femoris, vastus intermedius, gastrocnemius, and soleus were estimated via static optimization. Changes in muscle forces over the concentric phase were analyzed across loading conditions using statistical parametric mapping, impulse, and peak values. Conclusions about the effects of load differ between the three analysis methods; therefore, careful selection of analysis method is essential. Peaks may be inadequate in assessing differences in muscle force during dynamic movements. If SPM, assessing point-by-point differences, is combined with impulse, where time of force application is considered, both timepoint and overall loading can be analyzed. The response of individual muscle forces to increases in external load, as assessed by impulse and SPM, includes increased total muscle output, proportionally highest at 20%1RM, and increased absolute force for the vasti and plantarflexors during the concentric phase of hexbar jumps.

Peak Loads Associated With High-Impact Physical Activities in Children.

Physical activities involving impact loading are important for improving bone strength and mineral density in children. There is little research quantifying impact loads associated with various high-impact activities. PURPOSE: Examine the magnitude of peak ground reaction forces (pGRF) across different jumping activities in children. METHODS: Eight children between 8 and 12 years (9.63 [1.49] y; 1.42 [0.08] m; 33.69 [4.81] kg), performed 5 trials of a broad jump, countermovement jump, jumping jack, leap jump, and drop jump on a force plate. The pGRF were determined during the landing phase of each activity and expressed in units of body weight (BW). A repeated-measures analysis of variance was employed to assess differences in pGRF across activities. RESULTS: Drop jump exhibited the greatest pGRF (3.09 [0.46] BW) in comparison with the vertical jumping jack (2.56 [0.21] BW; P < .001) and countermovement jump (2.45 [0.22] BW; P = .001), as well as the horizontal broad jump (2.25 [0.2] BW; P = .003), and leap jump (2.01 [0.1] BW; P = .002). CONCLUSION: Peak loads between 2 and 3.1 BW were exhibited across each jump activity, which is moderate compared with magnitudes in most jump interventions seeking to improve bone health. All conditions except drop jump exhibited loading <3 BW, suggesting these activities may not produce sufficient loads to improve bone outcomes.

The effect of load based on body mass percentage on peak power output in the hang power clean, hang high pull, and mid-thigh clean pull.

BACKGROUND: Prescribing load at the peak power output (PPO) is one of the strategies utilized to enhance lower-body muscle power. PPO of an exercise is determined based on a relative percentage of the one-repetition maximum test (1RM). However, 1RM tests may be impractical in some weightlifting derivatives. This study aimed to identify the PPO of the hang power clean (HPC), hang high pull (HHP), and mid-thigh clean pull (MTCP) based on a relative percentage of body mass (BM). METHODS: Fifteen males with weightlifting experience performed HPC, HHP, and MTCP at loads ranging from 30-90% BM. Kinematic data were collected through a 16-camera infrared motion capture system and processed based on a three-dimensional lower-extremity model. Ground reaction force (GRF) data were collected from two force plates. PPO was calculated as the product of model center of mass velocity and combined vertical GRF during the concentric phase. RESULTS: PPO occurred at 90% BM for the HPC. In addition, the PPO occurred at 90% BM for the HHP and it was not different than 70% and 80% BM. At last, the PPO for MTCP occurred at 80% BM and it was not different than 60% and 70% BM. CONCLUSIONS: Relative percentages of BM can be used to determine PPO in the HPC, HHP, and MTCP. PPO during HPC is achieved at 90% BM, while the PPO for HHP and MTCP is achieved between 70% to 90% BM and 60 to 80% BM, respectively.

Leveraging virtual reality for vestibular testing: Clinical outcomes from tests of dynamic visual acuity.

BACKGROUND: Virtual reality (VR) use as a platform for vestibular rehabilitation is widespread. However, the utility of VR based vestibular assessments remains unknown. OBJECTIVE: To compare dynamic visual acuity (DVA) scores, perceived balance, and perceived dizziness when using traditional versus VR environments for DVA testing among healthy individuals. METHODS: DVA testing occurred for both a traditional clinical protocol and in a VR variant. Horizontal, vertical, and no head motion conditions were conducted for both clinical and VR test protocols. DVA scores, balance ratings, and dizziness ratings were obtained per condition. Two-way ANOVAs with repeated measures were used to assess differences in DVA scores, balance, and dizziness ratings. RESULTS: No differences in DVA results, balance or dizziness ratings were observed when comparing traditional clinical protocol versus the VR variant. Differences across head motion conditions were observed, with no motion trials exhibiting significantly higher DVA scores and perceived balance, and lower perceived dizziness compared to vertical and horizontal head motion. Vertical head motion exhibited this same trend compared to horizontal. CONCLUSION: DVA testing conducted in VR demonstrated clinical utility for each measure. Effects of head motion were similar across test variants, indicating DVA testing in VR produces similar effects on vestibular function than traditional clinical testing. Additional research should be conducted to assess the feasibility of VR assessment in individuals with vestibular disorder.

Lower-Extremity Motor Synergies in Individuals With and Without Chronic Ankle Instability.

Current theoretical models suggest that ankle sprain copers exhibit movement adaptations contributing to the avoidance of chronic ankle instability. However, few studies have examined adaptations at the level of biomechanical motor synergies. The purpose was to examine characteristics of the support moment synergy between individuals with chronic ankle instability, copers, and healthy individuals. A total of 48 individuals participated in the study. Lower-extremity kinetics and variability in the moment of force patterns were assessed during the stance phase of walking trials. The copers exhibited reductions in the support moment during the load response and preswing phase compared with the chronic ankle instability group, as well as during the terminal stance and preswing phase compared the healthy group. The copers also exhibited reductions in the hip extensor moment and ankle plantarflexion moment compared with healthy and chronic ankle instability groups during intervals of stance phase. Variability of the support moment and knee moment was greater in the copers compared with the chronic ankle instability group. Dampening of the support moment and select joint moments exhibited by the copers may indicate an adaptive mechanism to mitigate loading perturbations on the previously injured ankle. Heightened motor variability in copers may be indicative of a more adaptable motor synergy compared with individuals with chronic ankle instability.

Ankle Bracing Alters Coordination and Coordination Variability in Individuals With and Without Chronic Ankle Instability.

CONTEXT: Ankle bracing is an effective form of injury prophylaxis implemented for individuals with and without chronic ankle instability, yet mechanisms surrounding bracing efficacy remain in question. Ankle bracing has been shown to invoke biomechanical and neuromotor alterations that could influence lower-extremity coordination strategies during locomotion and contribute to bracing efficacy. OBJECTIVE: The purpose of this study was to investigate the effects of ankle bracing on lower-extremity coordination and coordination dynamics during walking in healthy individuals, ankle sprain copers, and individuals with chronic ankle instability. DESIGN: Mixed factorial design. SETTING: Laboratory setting. PARTICIPANTS: Forty-eight recreationally active individuals (16 per group) participated in this cross-sectional study. INTERVENTION: Participants completed 15 trials of over ground walking with and without an ankle brace. MAIN OUTCOME MEASURES: Coordination and coordination variability of the foot-shank, shank-thigh, and foot-thigh were assessed during stance and swing phases of the gait cycle through analysis of segment relative phase and relative phase deviation, respectively. RESULTS: Bracing elicited more synchronous, or locked, motion of the sagittal plane foot-shank coupling throughout swing phase and early stance phase, and more asynchronous motion of remaining foot-shank and foot-thigh couplings during early swing phase. Bracing also diminished coordination variability of foot-shank, foot-thigh, and shank-thigh couplings during swing phase of the gait cycle, indicating greater pattern stability. No group differences were observed. CONCLUSIONS: Greater stability of lower-extremity coordination patterns as well as spatiotemporal locking of the foot-shank coupling during terminal swing may work to guard against malalignment at foot contact and contribute to the efficacy of ankle bracing. Ankle bracing may also act antagonistically to interventions fostering functional variability.

Improving performance by anchoring movement and "nerves".

Golf's governing bodies' recent decision to ban all putting styles "anchoring one end of the club against the body" bridges an important practical problem with psychological theory. We report the first experiment testing whether anchoring provides technical and/or psychological advantage in competitive performance. Many "greats" of professional golf from Arnold Palmer and Jack Nicklaus to Tiger Woods have argued against anchoring, believing that it takes "nerves" out of competitive performance and therefore artificially levels the playing field. To shed more light on the issue, we tested participants' performance with anchored and unanchored putters under low and high pressure when controlling for the putter length. We found no statistically significant evidence for a technical advantage due to anchoring but a clear psychological advantage: participants who anchored their putters significantly outperformed unanchored counterparts under high, but not low, pressure. Results provide tentative evidence for the ban's justification from a competitive standpoint. However, before any definite conclusions can be made, more research is needed when using high-level golfers.

Post-exercise branched chain amino acid supplementation does not affect recovery markers following three consecutive high intensity resistance training bouts compared to carbohydrate supplementation.

BACKGROUND: Amino acid supplementation has been shown to potentially reduced exercise-induced muscle soreness. Thus, the purpose of this study was to examine if branched chain amino acid and carbohydrate (BCAACHO) versus carbohydrate-only sports drink (CHO) supplementation attenuated markers of muscle damage while preserving performance markers following 3 days of intense weight training. METHODS: Healthy resistance-trained males (n = 30) performed preliminary testing (T1) whereby they: 1) donated a baseline blood draw, 2) performed knee extensor dynamometry to obtain peak quadriceps isometric and isokinetic torque as well as electromyography (EMG) activity at 60°/s and 120°/s, and 3) performed a one repetition maximum (1RM) barbell back squat. The following week participants performed 10 sets x 5 repetitions at 80 % of their 1RM barbell back squat for 3 consecutive days and 48 h following the third lifting bout participants returned for (T2) testing whereby they repeated the T1 battery. Immediately following and 24 h after the three lifting bouts, participants were randomly assigned to consume one of two commercial products in 600 mL of tap water: 1) BCAAs and CHO (3 g/d L-leucine, 1 g/d L-isoleucine and 2 g/d L-valine with 2 g of CHO; n = 15), or 2) 42 g of CHO only (n = 15). Additionally, venous blood was drawn 24 h following the first and second lifting bouts and 48 h following the third bout to assess serum myoglobin concentrations, and a visual analog scale was utilized prior, during, and after the 3-d protocol to measure subjective perceptions of muscular soreness. RESULTS: There were similar decrements in 1RM squat strength and isokinetic peak torque measures in the BCAA-CHO and CHO groups. Serum myoglobin concentrations (p = 0.027) and perceived muscle soreness (p < 0.001) increased over the intervention regardless of supplementation. A group*time interaction was observed for monocyte percentages (p = 0.01) whereby BCAA-CHO supplementation attenuated increases in this variable over the duration of the protocol compared to CHO supplementation. CONCLUSION: BCAA-CHO supplementation did not reduce decrements in lower body strength or improve select markers of muscle damage/soreness compared to CHO supplementation over three consecutive days of intense lower-body training.