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A Baxter-Jones

Publications and source records attributed to A Baxter-Jones.

7 recordsLinked to original sources
PubMed2006

Change in lean body mass is a major determinant of change in areal bone mineral density of the proximal femur: a 12-year observational study.

Our objective was to assess the contribution of lean body mass (LBM) and fat body mass (FBM) to areal bone mineral density (aBMD) in women during the years surrounding menopause. We used a 12-year observational design. Participants included 75 Caucasian women who were premenopausal, 53 of whom were available for follow-up. There were two measurement periods: baseline and 12-year follow-up. At both measurement periods, bone mineral content and aBMD of the proximal femur, posterior-anterior lumbar spine, and total body was assessed using dual-energy X-ray absorptiometry (DXA). LBM and FBM were derived from the total-body scans. General health, including current menopausal status, hormone replace therapy use, medication use, and physical activity, was assessed by questionnaires. At the end of the study, 44% of the women were postmenopausal. After controlling for baseline aBMD, current menopausal status, and current hormone replacement therapy, we found that change in LBM was independently associated with change in aBMD of the proximal femur (P = 0.001). The cross-sectional analyses also indicated that LBM was a significant determinant of aBMD of all three DXA-scanned sites at both baseline and follow-up. These novel longitudinal data highlight the important contribution of LBM to the maintenance of proximal femur bone mass at a key time in women's life span, the years surrounding menopause.

Absorptiometry, Photon↗
PubMed1998

Modeling developmental changes in strength and aerobic power in children.

The present study examined two contrasting multilevel model structures to describe the developmental (longitudinal) changes in strength and aerobic power in children: 1) an additive polynomial structure and 2) a multiplicative structure with allometric body size components. On the basis of the maximum log-likelihood criterion, the multiplicative "allometric" model was shown to be superior to the additive polynomial model when fitted to the data from two published longitudinal studies and to provide more plausible solutions within and beyond the range of observations. The multilevel regression analysis of study 1 confirmed that aerobic power develops approximately in proportion to body mass, m1/3. The analyses from study 2 identified a significant increase in quadriceps and biceps strength, in proportion to body size, plus an additional contribution from age, centered at about peak height velocity (PHV). The positive "age" term for boys suggested that at PHV the boys were becoming stronger in the quadriceps and biceps in relation to their body size. In contrast, the girls' age term was either negligible (quadriceps) or negative (biceps), indicating that at PHV the girls' strength was developing in proportion to or, in the case of the biceps, was becoming weaker in relation to their body size.

Adolescent↗
PubMed1994

Age at menarche.

Explore the source record for details and available documents.

Adolescent↗
PubMed1993

Low injury rates in elite athletes.

A group of 453 elite young athletes (231 boys, 222 girls) in five two year age groups from 8-16 years of age was followed up for two years in order to identify self reported injuries over that period. Four sports were studied, namely football (soccer), gymnastics, tennis, and swimming. The injury rate was low with just over half the children suffering one or more injuries per year, with the majority of those injured sustaining one injury only. Over the two year period of intensive sporting activity this amounted to less than one injury per 1000 hours of training. The highest risk of injuries was in football (67%) and the lowest in swimming (37%). Most injuries (70%) were acute and of a minor nature, although overuse injuries did require longer periods off training and competition than acute injuries (20 v 13 days). Footballers appeared to sustain more significant injuries than other sports as judged by the time required to resume training and/or competition (16 days after acute and 57 after overuse). No significant associations were found between injury rate, injury severity, sex, and pubertal status with the single exception of female gymnasts in whom more injuries occurred in the latter stages of puberty. Only four of the 453 athletes reported injury as a reason for retiring from their chosen sports. Most injuries in elite young athletes are minor, their prevalence is low and, at least in the short to medium term, do not constitute a significant health problem.

Adolescent↗
PubMed1993

The development of aerobic power in young athletes.

Previous studies investigating the effects of training in children have been hampered in their interpretation by the confounding effects of growth and development. We followed the development of maximal aerobic power (VO2max) in 453 athletes drawn from soccer, swimming, gymnastics, and tennis. Study design was of a mixed longitudinal type with five age cohorts (8, 10, 12, 14 and 16 yr) followed for 3 consecutive years. A multilevel regression modeling procedure was used to identify the independent effects of predictor variables while accounting for the effects of growth, such as changes in body size. When age, height, and weight were controlled for, VO2max in males significantly increased with pubertal status, indicated by the coefficient value of 0.15 l/min being greater than its associated SE of 0.07 l/min. Females showed a similar pattern, with a coefficient value of 0.13 +/- 0.07 l/min, although the significant increase in VO2max (P < 0.05) found in males in the latter stages of puberty was not shown in females. Swimmers had the highest VO2max values (P < 0.001) at all ages.

Adolescent↗