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Scott J. Montain, Samuel N. Cheuvront and Henry C. Lukaski

Context:

Uncertainty exists regarding the effect of sustained sweating on sweat mineral-element composition.

Purpose:

To determine the effect of multiple hours of exercise-heat stress on sweat mineral concentrations.

Methods:

Seven heat-acclimated subjects (6 males, 1 female) completed 5 × 60 min of treadmill exercise (1.56 m/s, 2% grade) with 20 min rest between exercise periods in 2 weather conditions (27 °C, 40% relative humidity, 1 m/s and 35 °C, 30%, 1 m/s). Sweat was collected from a sweat-collection pouch attached to the upper back during exercise bouts 1, 3, and 5. Mineral elements were determined by using inductively coupled plasma-emission spectrography.

Results:

At 27 °C, sweat sodium (863 [563] µg/mL; mean [SD]), potassium (222 [48] µg/mL), calcium (16 [7]) µg/mL), magnesium (1265 [566] ng/mL), and copper (80 [56] ng/mL) remained similar to baseline over 7 h of exercise-heat stress, whereas sweat zinc declined 42–45% after the initial hour of exercise-heat stress (Ex1 = 655 [362], Ex3 = 382 [168], Ex5 = 355 [288] µg/mL, P < 0.05). Similar outcomes were observed for sweat zinc at 35 °C when sweat rates were higher. Sweat rate had no effect on sweat trace-element composition.

Conclusions:

Sweat sodium, potassium, and calcium losses during multiple hours of sustained sweating can be predicted from initial sweat composition. Estimates of sweat zinc losses, however, will be overestimated if sweat zinc conservation is not accounted for in sweat zinc-loss estimates.

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Xiaoya Ma, Kaitlyn J. Patterson, Kayla M. Gieschen and Peter F. Bodary

The prevalence of iron deficiency tends to be higher in athletic populations, especially among endurancetrained females. Recent studies have provided evidence that the iron-regulating hormone hepcidin is transiently increased with acute exercise and suggest that this may contribute to iron deficiency anemia in athletes. The purpose of this study was to determine whether resting serum hepcidin is significantly elevated in highly trained female distance runners compared with a low exercise control group. Due to the importance of the monocyte in the process of iron recycling, monocyte expression of hepcidin was also measured. A single fasted blood sample was collected midseason from twenty female distance runners averaging 81.9 ± 14.2 km of running per week. Ten age-, gender-, and BMI-matched low-exercise control subjects provided samples during the same period using identical collection procedures. There was no difference between the runners (RUN) and control subjects (CON) for serum hepcidin levels (p = .159). In addition, monocyte hepcidin gene expression was not different between the two groups (p = .635). Furthermore, no relationship between weekly training volume and serum hepcidin concentration was evident among the trained runners. The results suggest that hepcidin is not chronically elevated with sustained training in competitive collegiate runners. This is an important finding because the current clinical conditions that link hepcidin to anemia include a sustained elevation in serum hepcidin. Nevertheless, additional studies are needed to determine the clinical relevance of the well-documented, transient rise in hepcidin that follows acute sessions of exercise.

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Jeffrey J. Milroy, Stephen Hebard, Emily Kroshus and David L. Wyrick

seeking is delayed ( Asken, McCrea, Clugston, Snyder, & Houck, 2016 ). At present time, it is estimated that between 12% and 60% of athletes delay seeking care after sustaining a concussion. Differences in sport-related concussion (SRC) care seeking have been attributed to a number of different immutable

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Daniela Corbetta, Rebecca F. Wiener, Sabrina L. Thurman and Emalie McMahon

-proprioceptive unitary system, infants performed visually-triggered reaches where the sight of the target and the feel of their arm were undifferentiated. From that point on, researchers increasingly reported that infants sustained their visual fixations on the target and did not look at their hand during learning to

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Chantelle Zimmer, Janice Causgrove Dunn and Nicholas L. Holt

children at risk for DCD: (a) they hurt me, (b) it’s hard for me, and (c) I have to. The children talked about experiences in which they sustained psychological and physical harm from their peers, encountered difficulties in performing activities, and felt pressure to meet the teacher’s demands. They Hurt

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Zheng Wang, Peter C. M. Molenaar and Karl M. Newell

The experiment was set up to investigate the inter- and intrafoot coordination dynamics of postural control on balance boards. A frequency domain principal component analysis (PCA) was applied on 4 center of pressure (COP) time series collected from two force platforms to reveal their contributions to postural stability. The orientation of support played a more significant role than its width in channeling the foot coordination dynamics. When the support was oriented along the AP-challenging direction, the 4 COPs revealed a parallel contribution to the 1st principal component (PC1) indicating an interdependence of the foot coordination in both directions. When the support was positioned along the ML-challenging direction, the COPs in the AP direction showed larger weightings to PC1 implying an interfoot coordination. These findings provide evidence that COP coordination operates in adaptive ways to sustain postural stability in light of changing support constraints to standing.

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Shane R. Wurdeman, Jessie M. Huisinga, Mary Filipi and Nicholas Stergiou

Patients with multiple sclerosis (MS) have less-coordinated movements of the center of mass resulting in greater mechanical work. The purpose of this study was to quantify the work performed on the body’s center of mass by patients with MS. It was hypothesized that patients with MS would perform greater negative work during initial double support and less positive work in terminal double support. Results revealed that patients with MS perform less negative work in single support and early terminal double support and less positive work in the terminal double support period. However, summed over the entire stance phase, patients with MS and healthy controls performed similar amounts of positive and negative work on the body’s center of mass. The altered work throughout different periods in the stance phase may be indicative of a failure to capitalize on passive elastic energy mechanisms and increased reliance upon more active work generation to sustain gait.

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David M. Buchner and Paul H. Gobster

The purpose of this paper is to discuss the shared interest of the public health and parks and recreation sectors in promoting active visits to parks. At the institutional level, both sectors have missions to promote physical activity and view parks as key components in attaining physical activity goals. While some balancing among park goals may be necessary to avoid overuse and resource degradation, active visits more often complement park sustainability goals by reducing automobile and other motorized use impacts. The public health and parks and recreation sectors have each developed ecologic models to understand the determinants and outcomes of park-related physical activity. Transdisciplinary integration of these modeling efforts can lead to a better understanding of how active visits fit within the context of the overall recreational experience and the full range of benefits that parks provide. We conclude by identifying strategies for improving collaboration between the public health and parks and recreation sectors.

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Liria Akie Okai and André Fabio Kohn

Surprisingly little attention has been devoted to the role played by the intrinsic muscles of the human foot. The aim of this study was to quantify the capabilities of the flexor digitorum brevis (FDB) muscle to contribute to upright postural control. The approaches consisted of analysis of the effects of FDB contraction elicited by external electrical stimulation and quantification of the magnitude of FDB torque generation. The results showed the FDB can produce significant changes in static posture by itself as shown by changes in the center of pressure. Moreover, the FDB contribution to counterbalance the gravity’s toppling force was estimated at around 14.5% of the total required active torque at the ankle to keep the subject from falling. A posteriori functional analysis during horizontal perturbations showed high and self-sustained activity of FDB. These results demonstrated that the FDB has a significant capability of contributing to postural control.

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Michelle M. Porter, Miriam E. Nelson, Maria A. Fiatarone Singh, Jennifer E. Layne, Christine M. Morganti, Isaiah Trice, Christina D. Economos, Ronenn Roubenoff and William J. Evans

Resistance training (RT) increases strength in older adults, but there have been few studies of long-term RT or detraining in older adults. Postmenopausal participants (51–71 years of age) were randomized to RT or a control group for Year 1. For Year 2, participants chose whether to resistance train or not. Three groups emerged: train/train (n = 8: 60 ± 4 years), train/no train (n = 11: 62 ± 3 years), or controls (n = 17; 58 ± 6 years). Both training groups increased strength (p < .05) in Year 1. In Year 2, train/train maintained strength, whereas train/no train lost strength for knee extension (p < .001) but not for arm pulldown. Controls did not change. Reported physical activity levels were significantly increased in trainers in Year 1 and remained high regardless of RT in Year 2 (p < .05). Therefore, sustained changes in strength and physical activity behavior might be possible even if RT is discontinued.