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Janina M. Prado-Rico and Marcos Duarte

asymmetry will change over time. In a previous study, we indeed observed that postural changes are associated with asymmetry in the weight distribution between sides ( Prado, Dinato, & Duarte, 2011 ), but the body weight asymmetry during relaxed standing was never quantified. Whether humans have a prevalent

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Ben J. Lee and Charles Douglas Thake

The use of lower-body positive-pressure (LBPP) or body-weight-supported (BWS) exercise has become increasingly popular in rehabilitation and injury prevention settings. 1 – 4 A key benefit of applying LBPP is that cardiovascular fitness and lower limb function can be maintained, while the

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John A. Mercer, Bryon C. Applequist and Kenji Masumoto

Background:

Body-weight (BW) support during running can be accomplished using deep-water running (DWR; 100% BW support) and a lower-body positive-pressure (LBPP) treadmill.

Purpose:

To compare lower-extremity muscle activity during DWR and running on an LBPP treadmill at matched stride frequency.

Methods:

Eight subjects (40 ± 6.5 y, 173 ± 7.2 cm, 66.9 ± 11.7 kg) completed 4 running conditions all at a preferred stride frequency that was determined while running with no support. Two conditions were running on the LBPP treadmill at 60% and 80% of BW, and the other 2 conditions were different DWR styles: high knee (DWR-HK) and cross-country (DWR-CC). Average (AVG) and root-mean-square (RMS) electromyography (rectus femoris, biceps femoris, gastrocnemius, and tibialis anterior) were each compared among conditions (repeated-measures analysis of variance).

Results:

Results for AVG and RMS variables were identical for statistical tests for each muscle. Rectus femoris electromyography during DWR-HK was lower than that of DWR-CC (P < .05) but not different than either 60% BW or 80% BW (P > .05). Biceps femoris electromyography was less during DWR-HK than DWR-CC (P < .05) but greater during DWR-HK than either BW 60% or BW 80% (P < .05). Neither gastrocnemius nor tibialis anterior electromyography differed between conditions (P > .05).

Conclusion:

Neither the mechanism of BW support nor style of DWR influenced gastrocnemius or tibialis anterior muscle activity during running at the same stride frequency. However, rectus femoris and biceps femoris muscle activity were influenced by not only the mechanism of BW support but also the style of DWR.

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James Dziura, Stanislav V. Kasl and Loretta Di Pietro

Background:

It is not clear whether physical activity can exert a protective role on diabetes risk in older people that is independent of the changes in body weight that occur with both aging and disuse. The purpose of this analysis was to determine the relation between current physical activity, 3-year change in body weight, and the subsequent risk of type 2 diabetes in an older cohort.

Methods:

We studied prospectively 2,135 older (≥65 years) persons living in New Haven, CT, between 1982 and 1994. Physical activity was self-reported in 1982 and again in 1985; body weight and diabetes were self-reported annually over 12 years. Data were analyzed using multivariable Cox Proportional Hazards modeling with adjustments for age, sex, race, education, body mass index (BMI), smoking, chronic conditions, physical function, and alcohol intake.

Results:

Although an inverse graded relation was observed between level of activity and rate of diabetes, this dose–response relation did not reach statistical significance. However, older people who reported at least some activity at baseline experienced a significantly lower rate of diabetes between 1983 and 1994 compared to those reporting no activity (RR = 0.55; 95%CI = 0.35, 0.87). When 3-year changes in physical activity and body weight between 1982 and 1985 were added to the model, the relation between physical activity and reduced diabetes risk was unchanged (RR = 0.49; 95%CI = 0.24, 0.99).

Conclusions:

Even in advanced age, physical activity exerts an important and independent role in the prevention of type 2 diabetes. Continued physician counseling on the health effects of physical activity and referrals to community-based exercise programs should be encouraged among older people.

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Elizabeth M. Broad, Louise M. Burke, Greg R. Cox, Prue Heeley and Malcolm Riley

Fluid losses (measured by body weight changes) and voluntary fluid intakes were measured in elite basketball, netball, and soccer teams during typical summer and winter exercise sessions to determine fluid requirements and the degree of fluid replacement. Each subject was weighed in minimal clothing before and immediately after training, weights, and competition sessions; fluid intake, duration of exercise, temperature and humidity, and opportunity to drink were recorded. Sweat rates were greatest during competition sessions and significantly lower during weights sessions for all sports. Seasonal variation in dehydration (%DH) was not as great as may have been expected, particularly in sports played indoors. Factors influencing fluid replacement during exercise included provision of an individual water bottle, proximity to water bottles during sessions, encouragement to drink, rules of the game, duration and number of breaks or substitutions, and awareness of personal sweat rates. Guidelines for optimizing fluid intakes in these three sports are provided.

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Audrey R.C. Elias, Curt D. Hammill and Ryan L. Mizner

Though essential to athletic performance, the ability to land from a jump often remains limited following injury. While recommended, jump training is difficult to include in rehabilitation programs due to high impact forces. Body weight support (BWS) is frequently used in rehabilitation of gait following neurological and orthopedic injury, and may also allow improved rehabilitation of high-impact tasks. There is a differential effect of BWS on walking and running gaits, and the effect of BWS on movements with relatively large vertical displacement is unknown. The current study evaluates the effect of BWS on a replicable singleleg hopping task. We posited that progressive BWS would decrease limb loading while maintaining the joint kinematics of the task. Twenty-eight participants repetitively hopped on and off a box at each of four BWS levels. Peak vertical ground reaction forces decreased by 22.5% between 0% and 30% BWS (P < .001). Average hip, knee, and ankle internal moments decreased by 0.5 N·m/kg each. Slight kinematic changes across BWS levels were clinically insignificant. The high level of task specificity evidenced by consistent kinematics coupled with a similar reduction of internal moment at each joint suggests that BWS may be a useful strategy for rehabilitation of jumping tasks.

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Matthew F. Moran, Brendan J. Rickert and Beau K. Greer

Context:

Treadmills that unload runners via a differential air-pressure (DAP) bladder (eg, AlterG Anti-Gravity Treadmill) are commonly used to reduce effective body weight (BW) in a clinical setting. However, the relationship between the level of unloading and tibial stress is currently unknown.

Objective:

To determine the relationship between tibial impact acceleration and level of BW unloading during running.

Design:

Cross-sectional.

Setting:

University motion-analysis laboratory.

Participants:

15 distance runners (9 male, 6 female; 20.4 ± 2.4 y, 60.1 ± 12.6 kg).

Main Outcome Measures:

Peak tibial acceleration and peak-to-peak tibial acceleration were measured via a uniaxial accelerometer attached to the tibia during a 37-min continuous treadmill run that simulated reduced-BW conditions via a DAP bladder. The trial began with a 10-min run at 100% BW followed by nine 3-min stages where BW was systematically reduced from 95% to 60% in 5% increments.

Results:

There was no significant relationship between level of BW and either peak tibial acceleration or peak-to-peak tibial acceleration (P > .05). Both heart rate and step rate were significantly reduced with each 5% reduction in BW level (P < .01).

Conclusions:

Although ground-reaction forces are reduced when running in reduced-BW conditions on a DAP treadmill, tibial shock magnitudes are unchanged as an alteration in spatiotemporal running mechanics (eg, reduced step rate) and may nullify the unloading effect.

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Lenka Humenikova Shriver, Nancy Mulhollen Betts and Mark Edward Payton

Background:

Many wrestlers engage in chronic dieting and rapid “weight cutting” throughout the year to compete in a category below their natural weight. Such weightmanagement practices have a negative influence on their health and nutritional status, so the National Wrestling Coaches Association implemented a new weight-management program for high school wrestlers in 2006.

Purpose:

The purpose of this study was to determine whether seasonal changes in weight, body fat, and eating attitudes occur among high school wrestlers after the implementation of the new weight-management rule.

Methods:

Fifteen high school wrestlers participated in the study. Their weight, body composition, and eating attitudes were measured preseason, in-season, and off-season. Body fat was assessed using dual-energy X-ray absorptiometry. Attitudes toward dieting, food, and body weight were assessed using the Eating Attitude Test (EAT).

Results:

No significant changes in body fat were detected from preseason to off-season. Weight increased from preseason to in-season (p < .05) and off-season (p < .05). Although the EAT score did not change significantly from preseason to offseason, 60% reported “thinking about burning up calories when exercising” during preseason, and only 40% felt that way during the season (p < .05) and 47% during off-season (p < .05).

Conclusions:

The wrestlers experienced a significant weight gain from preseason to off-season with no significant changes in body fat. Their eating attitudes did not change significantly from preseason to off-season in this study, but further research using a large sample of high school wrestlers is warranted to confirm these findings.

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Georges Jabbour, Melanie Henderson, Angelo Tremblay and Marie Eve Mathieu

Objective:

Moderate-to-vigorous physical activity (MVPA) improves aerobic fitness in children, which is usually assessed by maximal oxygen consumption. However, other indices of aerobic fitness have been understudied.

Methods:

To compare net oxygen (VO2net), net energy consumption (Enet), net mechanical efficiency (MEnet), and lipid oxidation rate in active and inactive children across body weight statuses.

Design:

The sample included normal-weight, overweight, and obese children of whom 44 are active (≥30 min of MVPA/d) and 41 are inactive (<30 min of MVPA/d). VO2net, Enet, MEnet and lipid oxidation rate were determined during an incremental maximal cycling test.

Results:

Active obese participants had significantly lower values of VO2net and Enet and higher MEnet than inactive obese participants at all load stages. In addition, active obese participants showed a significantly higher lipid oxidation rate compared with inactive obese and active overweight and normal-weight participants. VO2net, Enet, and MEnet were similar across active children, regardless of body weight status.

Conclusion:

Thirty minutes or more of MVPA per day is associated with a potentiation of aerobic fitness indicators in obese prepubertal children. Moreover, the indices of aerobic fitness of inactive obese children are significantly different from those of active obese and nonobese ones.

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Lawrence Frank, Jacqueline Kerr, Dori Rosenberg and Abby King

Background:

Suburban development patterns may impede physical activity (PA) and mobility and affect healthy aging. This paper investigates the relationships between neighborhood design and walking, driving, PA, and obesity in adults over age 65 years.

Methods:

Data from the SMARTRAQ (Atlanta region) survey provided measures of PA, BMI, SES, and travel patterns. Neighborhood design was measured using a walkability index (residential density, street connectivity, retail density, and land use mix). Chi square and regression was used to evaluate relationships.

Results:

Increased walkability was related with more walking (OR 2.02), less time spent traveling in a car (OR .53), and lower odds of being overweight (OR .68). Those with 1 or no cars were more likely to walk (OR 2.9) and spend less time in cars (OR .53); but also less likely to get recommended levels of PA (OR .55). Visiting a fast food outlet was associated with increased odds of obesity (OR 1.81).

Conclusions:

Policies are needed to bring older Americans closer to shops and services and healthy food outlets as a means of encouraging regular walking and healthy body weight. Incentives to encourage neighborhood grocery stores and affordable housing in central areas along with regulatory reform through zoning can encourage PA and healthy body weight in the elderly.