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Panagiota Klentrou

Although osteoporosis is considered a geriatric disease, factors affecting bone strength are most influential during child growth and development. This article reviews what is known and still unclear in terms of bone growth, development and adaptation relative to physical activity before and during puberty. Bone is responsive to certain exercise protocols early in puberty and less so in postpubertal years, where bone strength, rather than bone mass, being the outcome of interest. Mechanical loading and high impact exercise promote bone strength. Intense training before and during puberty, however, may negatively affect bone development. Future research should focus on increasing our mechanistic understanding of the manner by which diverse physical stressors alter the integrity of bone. Longitudinal studies that examine the extent to which muscle and bone are comodulated by growth in children are also recommended.

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Panagiota Klentrou, Jill Slack, Brian Roy, and Michel Ladouceur

The effects of 12 wk of exercise training using weighted vests on bone turnover and isokinetic strength were evaluated in postmenopausal women randomly assigned as exercisers (EX; n = 9) or controls (CON; n = 7). Training included 3 multimodal exercise sessions per wk wearing weighted vests. The vest load was progressively increased each wk to a maximum of 15% of body weight. Bone turnover was determined from resting levels of serum osteocalcin and NTx. Knee and ankle strength were measured at 60°/s and 180°/s using an isokinetic dynamometer. After 12 wk, NTx decreased by 14.5% (P ≤ .05) in EX, with no significant changes in osteocalcin. EX also showed a 40% (P ≤ .05) improvement in ankle plantar-flexion strength at 60°/s. Relative body fat significantly decreased and fat-free mass increased in EX. Exercise compliance was 80%. These findings support the use of progressive exercise training using weighted vests in postmenopausal women.

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Panagiota Klentrou, Mary Lou Nishio, Michael Plyley, and Brock University

The purpose of this study was to compare the ventilatory breakpoints during exercise between young boys and adult men. Twenty-four active volunteers, 12 boys (10.8 ± 0.3 years of age) and 12 men (24.6 ± 1.1 years of age) with similar aerobic power (53.6 ± 4.2 to 55.7 ± 3.5 mlkg−1min−1), participated in the study. Each participant completed a standardized Physical Activity Questionnaire and anthropometric variables were measured. The exercise testing consisted of two graded tests to exhaustion on a treadmill. Heart rates were recorded every minute and gas exchange parameters were obtained every 30 s throughout the tests. Each ventilatory breakpoint was determined using a three-part model. Although the relative VO2peak values were not significantly different between the boys and the young adults, the boys reported significantly (p < .05) higher total activity than the adults. The boys had a significantly higher (p > .05) first ventilatory breakpoint expressed as a percentage of VO2peak than the adults (64.9% vs. 57.7%). Only 50% of the boys demonstrated a discernable VB2, and the VB2 of this group was not significantly different from that of the adults.

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Jennifer Dekker, Katlynne Nelson, Nigel Kurgan, Bareket Falk, Andrea Josse, and Panagiota Klentrou

This study examined resting levels of catabolic and anabolic osteokines related to Wnt signaling and their responses to a single bout of plyometric exercise in child and adolescent females. Fourteen premenarcheal girls [10.5 (1.8) y old] and 12 postmenarcheal adolescent girls [15.0 (1.0) y old] performed a plyometric exercise trial. One resting and 3 postexercise blood samples (5 min, 1 h, and 24 h postexercise) were analyzed for sclerostin, dickkopf-1 (DKK-1), osteoprotegerin (OPG), receptor activator of nuclear factor kappa-β ligand (RANKL), and transforming growth factors (TGF-β1, TGF-β2, and TGF-β3). Premenarcheal girls had significantly higher resting sclerostin, TGF-β1, TGF-β2, and TGF-β3 than the postmenarcheal girls, with no significant time effect or group-by-time interaction. DKK-1 was higher in premenarcheal compared with postmenarcheal girls. There was an overall significant DKK-1 decrease from baseline to 1 h postexercise, which remained lower than baseline 24 h postexercise in both groups. There was neither a significant group effect nor group-by-time interaction in OPG, RANKL, and their ratio. RANKL decreased 5 min postexercise compared with baseline and remained significantly lower from baseline 24 h following the exercise. No changes were observed in OPG. OPG/RANKL ratio was significantly elevated compared with resting values 1 h postexercise. In young females, high-impact exercise induces an overall osteogenic effect through a transitory suppression of catabolic osteokines up to 24 h following exercise.

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Izabella A. Ludwa, Bareket Falk, Matthew Yao, Lauren Corbett, and Panagiota Klentrou

This pilot study compared bone speed of sound (SOS), bone turnover and insulin-like growth factor 1 (IGF-1) between 20 Caucasian, postmenarcheal, adolescent synchronized swimmers (SS) and 20 aged- and maturity-matched nonswimmers (NS). Daily dietary intake and physical activity levels were also assessed. Bone SOS was measured by quantitative ultrasound. Blood samples were analyzed for osteocalcin, cross-linked N-teleopeptide of type I collagen (NTx), IGF-I and 25-OH vitamin D. Although no differences in bone SOS or turnover markers were observed between groups, the lower IGF-1 and vitamin D intake found in synchronized swimmers, in combination with their higher strenuous activity levels, should be further explored.

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Raffy Dotan, Cameron Mitchell, Rotem Cohen, Panagiota Klentrou, David Gabriel, and Bareket Falk

Children differ from adults in many muscular performance attributes such as size-normalized strength and power, endurance, fatigability and the recovery from exhaustive exercise, to name just a few. Metabolic attributes, such as glycolytic capacity, substrate utilization, and VO2 kinetics also differ markedly between children and adults. Various factors, such as dimensionality, intramuscular synchronization, agonist-antagonist coactivation, level of volitional activation, or muscle composition, can explain some, but not all of the observed differences. It is hypothesized that, compared with adults, children are substantially less capable of recruiting or fully employing their higher-threshold, type-II motor units. The review presents and evaluates the wealth of information and possible alternative factors in explaining the observations. Although conclusive evidence is still lacking, only this hypothesis of differential motor-unit activation in children and adults, appears capable of accounting for all observed child—adult differences, whether on its own or in conjunction with other factors.

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Aysha M. Thomas, Kayleigh M. Beaudry, Kimbereley L. Gammage, Panagiota Klentrou, and Andrea R. Josse

Background: Physical activity (PA) declines during early adulthood with higher rates of inactivity in university students. The authors aimed to examine the frequency, intensity, time, type of PA, and the barriers to PA participation in Canadian students during the first year of university. Methods: Questionnaires assessing PA variables were administered to 301 first-year students at the beginning and end of the academic year. Results: PA decreased over a year. Males engaged in more vigorous activity minutes, more strength training, and more organized sports than females (P < .05). Females participated in more fitness activities than males (P < .05). Intramural (noncompetitive and school organized) sport participation remained constant throughout the year. Significant intrapersonal barriers to PA engagement included stress and perceived self-skill; significant interpersonal barriers included lack of friends and peer influence; and significant structural barriers included homework, class schedule, and overcrowded facilities. Conclusion: PA and sport participation declined, and some differences existed between the sexes. Focus should be placed on reducing the barriers that students’ experience that may impact their PA. Interventions/programming to promote different aspects of PA should focus on noncompetitive sport and recreation activities, as well as activities that students can do on their own time. Ensuring the availability of adequate campus facilities is also important.

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Tony Adebero, Brandon John McKinlay, Alexandros Theocharidis, Zach Root, Andrea R. Josse, Panagiota Klentrou, and Bareket Falk

This study compared salivary and serum concentrations of testosterone and cortisol at rest and in response to intense multitask exercise in boys and men. Early morning saliva and venous blood samples were obtained before and 15 minutes after exercise from 30 competitive swimmers (15 boys, age 14.3 [1.9] y; 15 men, age 21.7 [3.1] y). Exercise included a swim-bench maximal strength task and an all-out 200-m swim, followed by a high-intensity interval swimming protocol (5 × 100 m, 5 × 50 m, and 5 × 25 m). At baseline, fasting testosterone (but not cortisol) concentration was higher in men than boys in serum and saliva (P < .05). Salivary and serum cortisol increased postexercise, with a greater increase in men compared with boys (men: 226% and 242%; boys: 78% and 64%, respectively; group by time interaction, P < .05). Testosterone was reduced postexercise in serum but not in saliva (men: −14.7% and 0.1%; boys: −33.9% and −4.5%, respectively, fluid by time interaction, P < .01). Serum and salivary cortisol (but not testosterone), preexercise and postexercise values were strongly correlated in both men and boys (r = .79 and .82, respectively; P < .01). In summary, early morning high-intensity exercise results in a decrease in testosterone in serum, but not saliva, and an increase in cortisol irrespective of the fluid used, in both boys and men. When examining immediate postexercise changes, the lack of correlation in testosterone between saliva and serum suggests that saliva may not be an appropriate fluid to examine changes in testosterone. The high correlation observed between serum and saliva for cortisol indicates that, in both boys and men, saliva may be used to monitor the immediate cortisol response to exercise.

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Bareket Falk, Sarah Braid, Michael Moore, Deborah O’Leary, Phil Sullivan, and Panagiota Klentrou

The objective of this study was to assess bone strength using quantitative ultrasound (QUS, Sunlight Omnisense) in pre- and early-pubertal normal weight (NW, % body fat ≤20, n = 28), and overweight (OW, % body fat ≥25, n = 15) boys. Groups were similar in chronological and skeletal age, sexual maturity, sports participation, and calcium intake. Leisure-time physical activity was lower in OW boys. Radial speed of sound (SOS) was similar in the two groups. Tibial SOS, however, was significantly lower in OW compared with NW (3,554 ± 109 vs. 3,646 ± 71 m·s−1, respectively). Among pre- and early-pubertal boys, higher adiposity appears to be associated with lower bone SOS in the lower extremities.

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Mathew Yao, Izabella Ludwa, Lauren Corbett, Panagiota Klentrou, Peter Bonsu, Kimberley Gammage, and Bareket Falk

Bone properties, reflected by speed of sound (SOS), and physical activity levels were examined in overweight (OW) girls (n = 19) and adolescents (n = 22), in comparison with normal-weight (NW) girls (n = 21) and adolescents (n = 13). Moderate-to-vigorous physical activity (MVPA) was higher in NW than in OW in both age groups. Tibial SOS was lower in OW compared with NW in both age groups. MVPA correlated with tibial SOS, once age was partialed out. The results suggest that overweight girls and adolescents are characterized by low tibial SOS, which may be partially attributed to lower physical activity levels.