Regulatory Light-Chain Phosphorylation During Weightlifting Training: Association With Postactivation Performance Enhancement

ABSTRACT

Chiu, LZF, Fry, AC, Galpin, AJ, Salem, GJ, and Cabarkapa, D. Regulatory light-chain phosphorylation during weightlifting training: association with postactivation performance enhancement. J Strength Cond Res 37(10): e563-e568, 2023-Postactivation performance enhancement has been reported for multijoint resistance exercise, with both neural and intrinsic muscle mechanisms suggested as contributing factors. The purpose of this investigation was to examine whether regulatory light-chain (RLC) phosphorylation in a primary mover is associated with enhanced weightlifting performance. Nine male athletes performed 15 sets of 3 repetitions of a multijoint weightlifting activity (clean pull) at 85% 1 repetition maximum. Measures of performance, peak barbell velocity (PV), and average barbell power (AP) were determined by video analysis. Muscle biopsies were taken within 30-60 seconds of completion of the previous lifting set from the vastus lateralis before (PRE), during (MID), and after (POST) a training session. AP was significantly greater for sets 3, 4, and 5 compared with set 1, with large effect sizes (0.8-1.0). Increases in PV did not reach significance; however, the effect size increase for sets 3 and 4 versus set 1 was moderate (0.4). Relative change scores for AP and RLC phosphorylation were positively and negatively correlated at MID (r = 0.60; p = 0.05) and POST (r = -0.74; p = 0.01) exercise, respectively. These data suggest that RLC phosphorylation initially may be associated with postactivation performance enhancement during repeated multijoint exercise.

Sex Difference in Hip Adduction during the Stance Phase of Running: A Swing Phase Problem?

PURPOSE

The purpose of the current study was 1) to evaluate sex differences in peak hip adduction during the late swing and stance phases of running and 2) to determine whether peak hip adduction during late swing is predictive of peak hip adduction during stance.

METHODS

A total of 15 female and 16 male heel strike runners ran over ground at a speed of 4 m·s-1. Hip joint kinematics during running were quantified using a 3D motion capture system. Sex differences in peak hip adduction during the late swing and stance phases were compared using independent-samples t-tests. Linear regression analysis was used to determine the relationship between late swing and stance phase hip adduction.

RESULTS

Compared with males, females exhibited significantly greater peak hip adduction during both the late swing (8.5° ± 2.6° vs 6.1° ± 2.8°, P = 0.019) and the stance phases of running (13.3° ± 4.2° vs 9.6° ± 3.4°, P = 0.011). Furthermore, late swing peak hip adduction was predictive of subsequent stance phase peak hip adduction (r = 0.63, P < 0.001).

CONCLUSION

Sex differences in hip adduction during stance are influenced in part by late swing phase hip adduction. Further studies are needed to identify potential causes of excessive hip adduction during the late swing phase of running.

Injury risk-factor differences between two golf swing styles: a biomechanical analysis of the lumbar spine, hip and knee

The golf swing has been associated with mechanical injury risk factors at many joints. One swing, the Minimalist Golf Swing, was hypothesised to reduce lumbar spine, lead hip, and lead knee ranges of motion and peak net joint moments, while affecting swing performance, compared to golfers' existing swings. Existing and MGS swings of 15 golfers with handicaps ranging from +2 to -20 were compared. During MGS downswing, golfers had 18.3% less lumbar spine transverse plane ROM, 40.7 and 41.8% less lead hip sagittal and frontal plane ROM, and 39.2% less lead knee sagittal plane ROM. MGS reduced lead hip extensor, abductor, and internal rotator moments by 17.8, 19.7 and 43%, while lead knee extensor, abductor, adductor and external rotator moments were reduced by 24.1, 26.6, 37 and 68.8% respectively. With MGS, club approach was 2° shallower, path 4° more in-to-out and speed 2 m/s slower. MGS reduced certain joint ROM and moments that are linked to injury risk factors, while influencing club impact factors with varying effect. Most golf injuries are from overuse, so reduced loads per cycle with MGS may extend the healthy life of joints, and permit golfers to play injury-free for more years.

In Standing, Corticospinal Excitability Is Proportional to COP Velocity Whereas M1 Excitability Is Participant-Specific

Reductions in the base of support (BOS) make standing difficult and require adjustments in the neural control of sway. In healthy young adults, we determined the effects of reductions in mediolateral (ML) BOS on peroneus longus (PL) motor evoked potential (MEP), intracortical facilitation (ICF), short interval intracortical inhibition (SICI) and long interval intracortical inhibition (LICI) using transcranial magnetic stimulation (TMS). We also examined whether participant-specific neural excitability influences the responses to increasing standing difficulty. Repeated measures ANOVA revealed that with increasing standing difficulty MEP size increased, SICI decreased (both p < 0.05) and ICF trended to decrease (p = 0.07). LICI decreased only in a sub-set of participants, demonstrating atypical facilitation. Spearman's Rank Correlation showed a relationship of ρ = 0.50 (p = 0.001) between MEP size and ML center of pressure (COP) velocity. Measures of M1 excitability did not correlate with COP velocity. LICI and ICF measured in the control task correlated with changes in LICI and ICF, i.e., the magnitude of response to increasing standing difficulty. Therefore, corticospinal excitability as measured by MEP size contributes to ML sway control while cortical facilitation and inhibition are likely involved in other aspects of sway control while standing. Additionally, neural excitability in standing is determined by an interaction between task difficulty and participant-specific neural excitability.

A pilot randomised controlled trial of a periodised resistance training and protein supplementation intervention in prostate cancer survivors on androgen deprivation therapy

INTRODUCTION

Prostate cancer survivors (PCS) receiving androgen deprivation therapy (ADT) experience deleterious side effects such as unfavourable changes in cardiometabolic factors that lead to sarcopenic obesity and metabolic syndrome (MetS). While loss of lean body mass (LBM) compromises muscular strength and quality of life, MetS increases the risk of cardiovascular disease and may influence cancer recurrence. Exercise can improve LBM and strength, and may serve as an alternative to the pharmacological management of MetS in PCS on ADT. Prior exercise interventions in PCS on ADT have been effective at enhancing strength, but only marginally effective at enhancing body composition and ameliorating cardiometabolic risk factors. This pilot trial aims to improve on existing interventions by employing periodised resistance training (RT) to counter sarcopenic obesity in PCS on ADT. Secondary aims compare intervention effects on cardiometabolic, physical function, quality of life and molecular skeletal muscle changes. An exploratory aim examines if protein supplementation (PS) in combination with RT elicits greater changes in these outcomes.

METHODS AND ANALYSIS

A 2×2 experimental design is used in 32 PCS on ADT across a 12-week intervention period. Participants are randomised to resistance training and protein supplementation (RTPS), RT, PS or control. RT and RTPS groups perform supervised RT three times per week for 12 weeks, while PS and RTPS groups receive 50 g whey protein per day. This pilot intervention applies a multilayered approach to ameliorate detrimental cardiometabolic effects of ADT while investigating molecular mechanisms underlying skeletal muscle changes in PCS.

ETHICS AND DISSEMINATION

This trial was approved by the University of Southern California Institutional Review Board (HS-13-00315). Results from this trial will be communicated in peer-reviewed publications and scientific presentations.

TRIAL REGISTRATION NUMBER

NCT01909440; Pre-results.

The Influence of a Bout of Exertion on Novice Barefoot Running Dynamics

Barefoot, forefoot strike (FFS) running has recently risen in popularity. Relative to shod, rear-foot strike (RFS) running, employing a FFS is associated with heightened triceps surae muscle activation and ankle mechanical demand. Novice to this pattern, it is plausible that habitually shod RFS runners exhibit fatigue to the triceps surae when acutely transitioning to barefoot running, thereby limiting their ability to attenuate impact. Therefore, the purpose was to determine how habitually shod RFS runners respond to an exertion bout of barefoot running, operationally defined as a barefoot run 20% of mean daily running distance. Twenty-one RFS runners performed novice barefoot running, before and after exertion. Ankle peak torque, triceps surae EMG median frequency, foot-strike patterns, joint energy absorption, and loading rates were evaluated. Of the 21 runners, 6 maintained a RFS, 10 adopted a mid-foot strike (MFS), and 5 adopted a FFS during novice barefoot running. In-response to exertion, MFS and FFS runners demonstrated reductions in peak torque, median frequency, and ankle energy absorption, and an increase in loading rate. RFS runners demonstrated reductions in peak torque and loading rate. These results indicate that a short bout of running may elicit fatigue to novice barefoot runners, limiting their ability to attenuate impact. Key pointsIn response to exertion, novice barefoot runners demonstrate fatigue to their soleus.In response to exertion, novice barefoot runners demonstrate a reduction in ankle energy absorptionIn response to exertion, novice barefoot runners demonstrate an increase in loading rate.

Lower limb dynamics vary in shod runners who acutely transition to barefoot running

Relative to traditional shod rear-foot strike (RFS) running, habituated barefoot running is associated with a forefoot-strike (FFS) and lower loading rates. Accordingly, barefoot running has been purported to reduce lower-extremity injury risk. Investigations, however, indicate that novice barefoot runners may not innately adopt a FFS. Therefore, the purpose of this study was to examine lower-extremity dynamics of habitually shod runners who acutely transition to barefoot running. 22 recreational RFS runners were included in this investigation. This laboratory controlled study consisted of two visits one-week apart, examining habitually shod, then novice barefoot running. Foot-strike patterns and loading rates were determined using motion analysis and force plates, and joint energy absorption was calculated using inverse dynamics. Of the 22 runners, 8 maintained a RFS, 9 adopted a MFS, and 5 adopted a FFS during novice barefoot running. All runners demonstrated a reduction in knee energy absorption when running barefoot; MFS and FFS runners also demonstrated a significant increase in ankle energy absorption. Runners who maintained a RFS presented with loading rates significantly higher than traditional shoe running, whereas FFS runners demonstrated a significant reduction in loading rate. Mid-foot strikers did not demonstrate a significant change in loading rate. These results indicate that habitually shod RFS runners demonstrate a variety of foot-strike and lower-extremity dynamic responses during the acute transition to barefoot running. Accordingly, explicit instruction regarding foot-strike patterns may be necessary if transitioning to barefoot. Long-term prospective studies are required in order to determine the influence of FFS barefoot running on injury rates.

The Trojan Lifetime Champions Health Survey: development, validity, and reliability

CONTEXT

Self-report questionnaires are an important method of evaluating lifespan health, exercise, and health-related quality of life (HRQL) outcomes among elite, competitive athletes. Few instruments, however, have undergone formal characterization of their psychometric properties within this population.

OBJECTIVE

To evaluate the validity and reliability of a novel health and exercise questionnaire, the Trojan Lifetime Champions (TLC) Health Survey.

DESIGN

Descriptive laboratory study.

SETTING

A large National Collegiate Athletic Association Division I university.

PATIENTS OR OTHER PARTICIPANTS

A total of 63 university alumni (age range, 24 to 84 years), including former varsity collegiate athletes and a control group of nonathletes.

INTERVENTION(S)

Participants completed the TLC Health Survey twice at a mean interval of 23 days with randomization to the paper or electronic version of the instrument.

MAIN OUTCOME MEASURE(S)

Content validity, feasibility of administration, test-retest reliability, parallel-form reliability between paper and electronic forms, and estimates of systematic and typical error versus differences of clinical interest were assessed across a broad range of health, exercise, and HRQL measures.

RESULTS

Correlation coefficients, including intraclass correlation coefficients (ICCs) for continuous variables and κ agreement statistics for ordinal variables, for test-retest reliability averaged 0.86, 0.90, 0.80, and 0.74 for HRQL, lifetime health, recent health, and exercise variables, respectively. Correlation coefficients, again ICCs and κ, for parallel-form reliability (ie, equivalence) between paper and electronic versions averaged 0.90, 0.85, 0.85, and 0.81 for HRQL, lifetime health, recent health, and exercise variables, respectively. Typical measurement error was less than the a priori thresholds of clinical interest, and we found minimal evidence of systematic test-retest error. We found strong evidence of content validity, convergent construct validity with the Short-Form 12 Version 2 HRQL instrument, and feasibility of administration in an elite, competitive athletic population.

CONCLUSIONS

These data suggest that the TLC Health Survey is a valid and reliable instrument for assessing lifetime and recent health, exercise, and HRQL, among elite competitive athletes. Generalizability of the instrument may be enhanced by additional, larger-scale studies in diverse populations.

Life span exercise among elite intercollegiate student athletes

Background:

Despite prominent public attention, data on life span health and exercise outcomes among elite, competitive athletes are sparse and do not reflect the diversity of modern athletes.

Hypothesis:

Life span exercise behavior differs between National Collegiate Athletic Association (NCAA) student athletes and a nonathlete control group. Sustained exercise is associated with improved cardiopulmonary health outcomes.

Study Design:

Cross-sectional, descriptive epidemiology study.

Level of Evidence:

Level 3.

Methods:

A total of 496 students and alumni (age range, 17-84 year) at a large, NCAA Division I university, including student athletes and an age- and sex-matched nonathlete control group, completed anonymous, self-report health and exercise questionnaires. Age-stratified, cross-sectional analysis evaluated previous week’s total exercise volume (ExVol), self-rated exercise importance (ExImp), and compliance with American College of Sports Medicine (ACSM) exercise guidelines for healthy adults. The association of ACSM guideline compliance with lifetime cardiopulmonary health outcomes was also assessed.

Results:

Current student athletes reported significantly greater ExVol (P < 0.001. Cohen d = 0.99, probability of clinically important difference [pCID] >99.5%), ExImp (P < 0.001, d = 1.96, pCID = 96%), and likelihood of compliance with ACSM guidelines (odds ratio [OR], 95% confidence interval [CI] = 30.6, 11.0-84.6) compared with nonathletes. No significant differences were found between alumni student athletes and nonathletes. Alumni student athletes demonstrated substantially lower ExVol (P < 0.001, d = –0.94, pCID >99.5%) and guideline compliance (OR = 0.09, 95% CI = 0.05-0.19) compared with current student athletes, whereas nonathletes had similar exercise behavior across the life span. Among alumni, ACSM guideline compliance was associated with significant attenuation of cardiopulmonary health concerns (P = 0.02, d = –0.50, pCID = 14%) independent of intercollegiate athletic participation.

Conclusion:

Although current NCAA Division I student athletes demonstrated significant, clinically important differences in exercise behavior compared with nonathletes, no group differences were evident later in life. Irrespective of collegiate athletic status, healthy exercise behavior among alumni was associated with cardiopulmonary health benefits.

Clinical Relevance:

To realize life span health benefits, it is imperative that student athletes maintain consistent patterns of healthy exercise beyond retirement from competitive sports.

The association between unilateral heel-rise performance with static and dynamic balance in community dwelling older adults

As a measure of both strength and muscle endurance of the plantar flexors, the unilateral heel rise (UHR) test has been suggested as a method to evaluate balance capabilities in older adults. Thus, the purpose of this study was to examine the association between UHR performance with biomechanical measures of balance in seniors. Twenty-two older adults completed two testing sessions. The first visit included UHR performance; the second visit included dynamic and static motion analysis. UHR performance was significantly associated with dynamic balance capability as measured by medial-lateral inclination angle during gait. As indicated by an analysis of center of pressure, there were significant associations between UHR performance and measures of static balance. Balance is influenced by plantar flexor performance as measured by the UHR test. We therefore suggest incorporating the UHR test in analyses of balance in seniors.

Holistic life-span health outcomes among elite intercollegiate student-athletes

CONTEXT

Competitive sports are recognized as having unique health benefits and risks, and the effect of sports on life-span health among elite athletes has received increasing attention. However, supporting scientific data are sparse and do not represent modern athletes.

OBJECTIVE

To assess holistic life-span health and health-related quality-of-life (HRQL) among current and former National Collegiate Athletic Association student-athletes (SAs).

DESIGN

Cross-sectional study.

SETTING

A large Division I university.

PATIENTS OR OTHER PARTICIPANTS

Population-based sample of 496 university students and alumni (age 17-84 years), including SAs and an age-matched and sex-matched nonathlete (NA) control group.

MAIN OUTCOME MEASURE(S)

Participants completed anonymous, self-report questionnaires. We measured the Short-Form 12 (SF-12) physical and mental component HRQL scores and cumulative lifetime experience and relative risk of treatment for joint, cardiopulmonary, and psychosocial health concerns.

RESULTS

Older alumni (age 43+ years) SAs reported greater joint health concerns than NAs (larger joint summary scores; P = .04; Cohen d = 0.69; probability of clinically important difference [pCID] = 77%; treatment odds ratio [OR] = 14.0, 95% confidence interval [CI] = 1.6, 126). Joint health for current and younger alumni SAs was similar to that for NAs. Older alumni reported greater cardiopulmonary health concerns than younger alumni (summary score P < .001; d = 1.05; pCID = 85%; OR = 5.8, 95% CI = 2.0, 16) and current students (P < .001; d = 2.25; pCID >99.5%; OR = 7.1, 95% CI = 3.3, 15), but the risk was similar for SAs and NAs. Current SAs demonstrated evidence of better psychosocial health (summary score P = .006; d = -0.52; pCID = 40%) and mental component HRQL (P = .008; d = 0.50; pCID = 48%) versus NAs but similar psychosocial treatment odds (OR = 0.87, 95% CI = 0.39, 1.9). Psychosocial health and mental component HRQL were similar between alumni SAs and NAs. No differences were observed between SAs and NAs in physical component HRQL.

CONCLUSIONS

The SAs demonstrated significant, clinically meaningful evidence of greater joint health concerns later in life, comparable cardiopulmonary health, and differences in life-span psychosocial health and HRQL profiles compared with NAs. These data provide timely evidence regarding a compelling public issue and highlight the need for further study of life-span health among modern athletes.

A comparison of dorsal and heel plate foot tracking methods on lower extremity dynamics

The primary method to model ankle motion during inverse dynamic calculations of the lower limb is through the use of skin-mounted markers, with the foot modeled as a rigid segment. Motion of the foot is often tracked via the use of a marker cluster triad on either the dorsum, or heel, of the foot/shoe. The purpose of this investigation was to evaluate differences in calculated lower extremity dynamics during the stance phase of gait between these two tracking techniques. In an analysis of 7 subjects, it was found that sagittal ankle angles and sagittal ankle, hip and knee moments were strongly correlated between the two conditions, however, there was a significant difference in peak ankle plantar flexion and dorsiflexion angles. Frontal ankle angles were only moderately correlated and there was a significant difference in peak ankle eversion and inversion, resulting in moderate correlations in frontal plane moments and a significant difference in peak hip adductor moments. We demonstrate that the technique used to track the foot is an important consideration in interpreting lower extremity dynamics for clinical and research purposes.

Yoga Improves Upper-Extremity Function and Scapular Posturing in Persons with Hyperkyphosis

OBJECTIVE

Hyperkyphosis (excess thoracic spine curvature) is associated with upper-extremity functional limitations and altered scapular posturing. The purpose of this study was to quantify the changes in upper-extremity function and scapular posturing following a 6-month yogaintervention in persons with hyperkyphosis.

METHODS

Twenty-one older adults with hyperkyphosis (75.5+7.4 yrs) enrolled in the UCLA Yoga for Kyphosis randomized controlled trial, elected to participate in this uncontrolled, prepost substudy of upper-extremity function. They were measured at baseline and after a 24-week yoga intervention. Maximum vertical reach and timed book tests were used to evaluate upper-extremity function. Scapular posturing was quantified using a motion analysis system and data was obtained under 4 conditions: 1) quiet-standing, 2) normal walking, 3) fast walking, and 4) seated. Paired t-tests were used to test for changes between baseline and 6-month follow-up measures and Cohen's d was calculated to examine effect sizes.

RESULTS

Following the 6-month yoga intervention, participants improved their book test performance by 26.4% (p < 0.001; d = 1.5). Scapular protraction decreased by 2.9% during the static-sitting condition (p < 0.001; d = 0.5) and the overall excursion of the scapulae decreased for both fast (25.0%, p < 0.05; d = 0.6) and self-selected walking (29.4%, p < 0.01; d = 0.9). There were no changes in maximum vertical reach.

CONCLUSION

Subjects demonstrated significant improvements with small to large effect sizes in the timed book test and scapular posturing to a less protracted position during both static and dynamic conditions after the intervention. These adaptations are likely to reduce the risk of scapular impingement and help preserve functional independence in older adults.

The Relationships Between the Unified Parkinson’s Disease Rating Scale and Lower Extremity Functional Performance in Persons With Early-Stage Parkinson’s Disease

Background. The Unified Parkinson’s Disease Rating Scale (UPDRS) is the “gold standard” assessment tool for characterizing impairments in persons with Parkinson’s disease (PD); however, this scale’s ability to predict functional capabilities across different functional tasks has not been adequately assessed in persons with early-stage PD. Methods. Thirty persons with PD within 3 years of diagnosis and without motor fluctuation performed self-selected walking, fast walking, and sit-to-stand and stair-climbing tasks. Pearson’s correlation coefficients were used to calculate correlations with a standard UPDRS examination ( P < .05). Simple linear regression models were used to fit each functional performance outcome measure with the UPDRS total predictor scores. Results. The correlations between the UPDRS motor (section III), UPDRS total scores, and all timed functional performance measures were fair to good (range, 0.45-0.57). Conversely, only greater self-selected time to walk 50 ft correlated with a higher UPDRS activities of daily living (II) score ( r = .386; P < .05). Conclusions. The UPDRS motor (III) and total scores may be good predictors of overall lower extremity function in persons with early-stage PD. Understanding the relationships between UPDRS scores and functional capabilities may allow clinicians to better quantify early physical functioning, longitudinally assess disease progression, and assess the efficacy of interventions.

Bilateral differences in the net joint torques during the squat exercise

Bilateral movements are common in human movement, both as exercises and as daily activities. Because the movement patterns are similar, it is often assumed that there are no bilateral differences (BDs; differences between the left and right sides) in the joint torques that are producing these movements. The aim of this investigation was to test the assumption that the joint torques are equal between the left and right lower extremities by quantifying BDs during the barbell squat. Eighteen recreationally trained men (n = 9) and women (n = 9) completed 3 sets of 3 repetitions of the squat exercise, under 4 loading conditions: 25, 50, 75, and 100% of their 3 repetition maximum, while instrumented for biomechanical analysis. The average net joint moment (ANJM) and maximum flexion angle (MFA) for the hip, knee, and ankle as well as the average vertical ground reaction force (AVGRF) and the average distance from the ankle joint center to the center of pressure (ADCOP) were calculated. Group mean and individual data were analyzed (alpha = 0.05). At each joint, there was a significant main effect for side and load, no main effect for gender, with few significant interactions. The hip ANJM was 12.4% larger on the left side, the knee ANJM was 13.2% larger on the right side, and the ankle ANJM was 16.8% larger on the left side. Differences in MFAs between sides were less than 2 degrees for all 3 joints (all p > 0.20 except for the knee at 75% [p = 0.024] and 100% [p = 0.025]), but the AVGRF and the ADCOP were 6% and 11% larger on the left side. Few subjects exhibited the pattern identified with the group mean data, and no subject exhibited nonsignificant BDs for all 3 joints. These findings suggest that joint torques should not be assumed to be equal during the squat and that few individual subjects follow the pattern exhibited by group mean data.

The effect of exercise training in improving motor performance and corticomotor excitability in people with early Parkinson's disease

OBJECTIVES

To obtain preliminary data on the effects of high-intensity exercise on functional performance in people with Parkinson's disease (PD) relative to exercise at low and no intensity and to determine whether improved performance is accompanied by alterations in corticomotor excitability as measured through transcranial magnetic stimulation (TMS).

DESIGN

Cohort (prospective), randomized controlled trial.

SETTING

University-based clinical and research facilities.

PARTICIPANTS

Thirty people with PD, within 3 years of diagnosis with Hoehn and Yahr stage 1 or 2.

INTERVENTIONS

Subjects were randomized to high-intensity exercise using body weight-supported treadmill training, low-intensity exercise, or a zero-intensity education group. Subjects in the 2 exercise groups completed 24 exercise sessions over 8 weeks. Subjects in the zero-intensity group completed 6 education classes over 8 weeks.

MAIN OUTCOME MEASURES

Unified Parkinson's Disease Rating Scales (UPDRS), biomechanic analysis of self-selected and fast walking and sit-to-stand tasks; corticomotor excitability was assessed with cortical silent period (CSP) durations in response to single-pulse TMS.

RESULTS

A small improvement in total and motor UPDRS was observed in all groups. High-intensity group subjects showed postexercise increases in gait speed, step and stride length, and hip and ankle joint excursion during self-selected and fast gait and improved weight distribution during sit-to-stand tasks. Improvements in gait and sit-to-stand measures were not consistently observed in low- and zero-intensity groups. The high-intensity group showed lengthening in CSP.

CONCLUSIONS

The findings suggest the dose-dependent benefits of exercise and that high-intensity exercise can normalize corticomotor excitability in early PD.

Comparison of joint kinetics during free weight and flywheel resistance exercise

The most common modality for resistance exercise is free weight resistance. Alternative methods of providing external resistance have been investigated, in particular for use in microgravity environments such as space flight. One alternative modality is flywheel inertial resistance, which generates resistance as a function of the mass, distribution of mass, and angular acceleration of the flywheel. The purpose of this investigation was to characterize net joint kinetics of multijoint exercises performed with a flywheel inertial resistance device in comparison to free weights. Eleven trained men and women performed the front squat, lunge, and push press on separate days with free weight or flywheel resistance, while instrumented for biomechanical analysis. Front squats performed with flywheel resistance required greater contribution of the hip and ankle, and less contribution of the knee, compared to free weight. Push presses performed with flywheel resistance had similar impulse requirements at the knee compared to free weight, but greater impulse requirement at the hip and ankle. As used in this investigation, flywheel inertial resistance increases the demand on the hip extensors and ankle plantarflexors and decreases the mechanical demand on the knee extensors for lower extremity exercises such as the front squat and lunge. Exercises involving dynamic lower and upper extremity actions, such as the push press, may benefit from flywheel inertial resistance, due to the increased mechanical demand on the knee extensors.

Relationships among body weight, joint moments generated during functional activities, and hip bone mass in older adults

OBJECTIVE

To investigate the relationships among hip joint moments produced during functional activities and hip bone mass in sedentary older adults.

METHODS

Eight male and eight female older adults (70-85 yr) performed functional activities including walking, chair sit-stand-sit, and stair stepping at a self-selected pace while instrumented for biomechanical analysis. Bone mass at proximal femur, femoral neck, and greater trochanter were measured by dual-energy X-ray absorptiometry. Three-dimensional hip moments were obtained using a six-camera motion analysis system, force platforms, and inverse dynamics techniques. Pearson's correlation coefficients were employed to assess the relationships among hip bone mass, height, weight, age, and joint moments. Stepwise regression analyses were performed to determine the factors that significantly predicted bone mass using all significant variables identified in the correlation analysis.

FINDINGS

Hip bone mass was not significantly correlated with moments during activities in men. Conversely, in women bone mass at all sites were significantly correlated with weight, moments generated with stepping, and moments generated with walking (p<0.05 to p<0.001). Regression analysis results further indicated that the overall moments during stepping independently predicted up to 93% of the variability in bone mass at femoral neck and proximal femur; whereas weight independently predicted up to 92% of the variability in bone mass at greater trochanter.

INTERPRETATION

Submaximal loading events produced during functional activities were highly correlated with hip bone mass in sedentary older women, but not men. The findings may ultimately be used to modify exercise prescription for the preservation of bone mass.

Cardiovascular fitness and physical activity in children with and without impaired glucose tolerance

OBJECTIVE

To examine differences in cardiovascular fitness (VO(2max)) and physical activity levels in overweight Hispanic children with normal glucose tolerance (NGT) vs impaired glucose tolerance (IGT).

PARTICIPANTS

A total of 173 overweight (BMI percentile 97.0 +/- 3.1) Hispanic children ages 8-13 years with a family history of type 2 diabetes.

METHODS

VO(2max) was measured via a maximal effort treadmill test and open circuit spirometry. Physical activity was determined by questionnaire. Glucose tolerance was established by a 2-h oral glucose challenge (1.75 g of glucose/kg body weight). IGT was defined from an oral glucose tolerance test as a 2-h plasma glucose level > or =140 and <200 mg/dl.

RESULTS

IGT was detected in 46 of the 173 participants (approximately 27%); no cases of type 2 diabetes were identified. No significant differences were found between youth with NGT and those with IGT in absolute VO(2max) (2.2 +/- 0.6 vs 2.1 +/- 0.5 l/min), VO(2max) adjusted for gender, age, and body composition (2.2 +/- 0.2 vs 2.1 +/- 0.2 l/min), or recreational physical activity levels (8.7 +/- 8.2 vs 6.9 +/- 6.2 h/week).

CONCLUSION

Overweight Hispanic youth with IGT exhibit similar levels of VO(2max) and physical activity compared to their NGT counterparts. Longitudinal analyses are necessary to determine whether fitness/activity measures contribute significantly to diabetes risk over time in this group.

Effects of Resistance Training on Insulin Sensitivity in Overweight Latino Adolescent Males

PURPOSE

Insulin resistance is thought to be a core defect in the pathophysiology of obesity-related comorbidities in children, such as type 2 diabetes. Exercise training is known to improve insulin resistance and reduce the risk of type 2 diabetes in adults. However, very little is known regarding the effects of exercise on insulin resistance in youth. Therefore, we examined the effects of a 16-wk resistance training exercise intervention on insulin sensitivity in youth at high risk for developing type 2 diabetes.

METHODS

Twenty-two overweight Latino adolescent males were randomly assigned to either a twice-per-week resistance training group (RT=11) or a nonexercising control group (C=11) for 16 wk. Strength was assessed by one-repetition maximum, body composition was quantified by dual-energy x-ray absorptiometry, and insulin sensitivity was determined by the frequently sampled intravenous glucose tolerance test with minimal modeling.

RESULTS

Significant increases in upper- and lower-body strength were observed in the RT compared with the C group. The RT group significantly increased insulin sensitivity compared with the C group (P<0.05), and this increase remained significant after adjustment for changes in total fat mass and total lean tissue mass (P<0.05). Compared with baseline values, insulin sensitivity increased 45.1+/-7.3% in the RT group versus -0.9+/-12.9% in controls (P<0.01).

CONCLUSION

A twice-per-week 16-wk resistance training program can significantly increase insulin sensitivity in overweight Latino adolescent males independent of changes in body composition.

Biomechanics of the heel-raise exercise

The purpose of this investigation was to determine whether increases in internal (muscular) demand would be proportional to increases in the external demand during heel-raise exercise. Seven male (mean age 74.9 +/- 4.8 years) and 9 female (mean age 74.4 +/- 5.1 years) older adults performed both double-leg heel raises and single-leg heel raises under 3 loading conditions (no external resistance and +5% and +10% of each participant's body weight). Kinematic and kinetic dependent variables were calculated using standard inverse-dynamics techniques. The results suggest that although the single-heel raise led to increases in peak net joint moments, power, and mechanical-energy expenditure (MEE), it did so at the expense of range of motion and angular velocity. In addition, increasing the external resistance by 5% of participants' body weight did not elicit significant changes in either the power or the MEE of the ankle joint. These effects should be considered when prescribing these exercises to older adults.

Cardiovascular fitness and the metabolic syndrome in overweight latino youths

PURPOSE

To determine whether cardiovascular fitness (.)VO(2max) is associated with the metabolic syndrome and its individual features in overweight Latino youths.

METHODS

A total of 163 overweight Latino boys and girls (body mass index (BMI) percentile = 97.0 +/- 3.1; age = 11.2 +/- 1.7 yr) with a family history of Type 2 diabetes participated in this investigation. The metabolic syndrome was defined as having three or more of the following risk factors: abdominal obesity, high blood pressure, low HDL-cholesterol, high triglycerides, and impaired glucose tolerance. (.)VO(2max) was determined by a progressive treadmill test to exhaustion, and body composition was assessed using dual energy x-ray absorptiometry.

RESULTS

(.)VO(2max) was not correlated with any individual risk factor of the metabolic syndrome after adjusting for gender, age, and body composition in partial analysis. Furthermore, ANCOVA revealed that children with zero, one, two, or three or more risk factors did not differ in regards to fitness levels.

CONCLUSION

(.)VO(2max) is not independently associated with the metabolic syndrome or any individual feature in overweight youths of Latino ethnicity after controlling for differences in confounding variables.

Biomechanical attributes of lunging activities for older adults

The purpose of this study was to characterize the mechanical demands of the lower-extremity musculature during the standing forward lunge (FL) and the standing lateral lunge (LL) exercises performed by older adults. Twenty healthy older adults (9 men, 11 women, mean age 75.0 +/- 4.4 years) performed FL and LL while instrumented for biomechanical analysis. Lower-extremity net joint moments, powers, impulse, and mechanical energy expenditure were determined using standard inverse dynamics techniques. The FL preferentially targeted the hip extensors, producing a greater flexion angle (12.8%), peak joint moment (13.6%), joint power (56.5%), and mechanical energy expenditure (25.1%). Conversely, LL targeted the ankle plantar flexors, producing greater dorsiflexion angles (19.3%), joint moments (40.9%), impulse (87.0%), and mechanical energy expenditure (61.1%). Kinetic differences at the knee were less consistent. Fitness professionals may use this information to better match the biomechanical attributes of FL and LL activities with the needs of the trainee.

The relations among upper-extremity loading characteristics and bone mineral density changes in young women

The relations among the reaction forces engendered during an upper-extremity dynamic impact-loading exercise (DILE) program and bone mineral density adaptations (DeltaBMD) in the radius were investigated in 24 healthy premenopausal women (mean age = 29 +/- 6 years). Subjects performed DILE 36 cycles/day, 3 days/week for 24 weeks. The exercised arm was allocated randomly to either the dominant or the nondominant limb. In addition, subjects were assigned randomly into either damped or nondamped treatment arms to examine the effects of both higher- and lower-magnitude loading prescriptions. Measurements including anthropometrics, self-reported physical activity levels, hand-grip strength, radial BMD (DEXA, Hologic QDR1500, MA) at the ultradistal radius (UD), distal 1/3 radius (DR), and total distal radius (TOTAL), and exercise-related loading characteristics (impact load, loading rate, and impulse) were recorded at baseline and at 6 months. Simple linear regression models were used to fit the regional BMD changes to the reaction force, changes in hand-grip strength (DeltaGRIP), and changes in body weight (DeltaBW). Findings demonstrated that the damping condition utilized during DILE influenced the relations between loading events and BMD changes. Specifically, none of the reaction-force characteristics significantly predicted changes in BMD in participants performing DILE using the damped condition, whereas, in the nondamped condition, impact load accounted for 58% of the variance in BMD change at DR and 66% of the variance in BMD change at TOTAL. Thresholds of 345 and 285 N of impact force to promote BMD increases at DR and TOTAL, respectively, were obtained from the regression models in the nondamped group. Impulse was also an independent predictor of BMD changes at TOTAL, accounting for 56% of the variance. Neither DeltaGRIP nor DeltaBW significantly predicted DeltaBMD at any radial site. These findings, in young adult women, parallel previous reports identifying significant, regionally specific relations among external loading events and BMD changes in both animal and human models.