Kristin S. Ondrak

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A calibration study was conducted to determine the threshold counts for two commonly used accelerometers, the ActiGraph and the Actical, to classify activities by intensity in children 5 to 8 years of age. Thirty-three children wore both accelerometers and a COSMED portable metabolic system during 15 min of rest and then performed up to nine different(More)
Osteoporosis is a serious and potentially debilitating disease, which can lead to a variety of health complications and a diminished quality of life. Consequently, the development of bone mineral density (BMD) and content (BMC) during childhood and adolescence is of great importance, as it may attenuate the effects and incidence of osteoporosis later in(More)
OBJECTIVE To determine the effect of oral contraceptives (OC) on hamstring neuromechanics and lower extremity stiffness across the menstrual cycle (MC). DESIGN Causal comparative. SETTING Research laboratory. PARTICIPANTS Thirty, healthy, normally menstruating female volunteers who were using OC (OC group, n = 15) or not (non-OC group, n = 15). (More)
OBJECTIVE While acute alterations in leptin, insulin, cortisol and growth hormone (GH) levels have been reported in children following weight change interventions, little is known about natural hormonal changes as children grow and how these changes are affected by unprovoked weight status changes. The purpose of this investigation was to compare changes in(More)
Research on obese adults has shown that their ventilatory dynamics differ from normal weight adults; however, the ventilatory dynamics of obese and non-obese children have never been documented. Thus, the ventilatory responses of 73 overweight youth (BMI >85th percentile) were compared to 73 age, sex and height-matched normal weight youth (BMI <85th(More)
PURPOSE To describe how the relationships between aerobic power or percent body fat and cardiovascular disease (CVD) risk differ by age. METHODS A sample of 1,824 young persons was divided into age groups (8-10, 11-13, and 14-16 years). Aerobic power (VO(2)max) was predicted using a submaximal cycle ergometer test, whereas percent body fat was assessed(More)
PURPOSE The effect of exercise intensity on the tracking of serum and salivary cortisol responses was examined in 12 endurance-trained males (maximal oxygen uptake [VO2max] = 58.2 ± 6.4 mL/kg/min). METHODS Subjects rested for 30 min (control) and exercised on a cycle ergometer for 30 min at 40% (low), 60% (moderate), and 80% (high intensity) of VO2max on(More)
The influences of sex, age, exercise intensity, and end-tidal CO2 on the inspiratory drive ([V T kg−1]·T i −1) and respiratory timing (T i·T tot −1) components of ventilation were examined in 295 youth (138 females, 157 males); similarly distributed 8–18 years of age. Ventilatory and metabolic measures were collected breath-by-breath at rest and during a(More)
Hormonal fluctuations are one potential reason why females might have a greater rate of noncontact ACL injury. The hamstrings are capable of limiting anterior cruciate ligament (ACL) loading. This study examined whether relationships existed between reproductive hormones (estradiol-β-17, free testosterone, and progesterone) and hamstring neuromechanical(More)
The management of concussion and mild traumatic brain injury is an area of clinical uncertainty for many sports medicine professionals. While recent studies suggest sex differences in neurocognitive function may exist, our understanding of the effects of menstrual cycle phase and oral contraceptive pill (OCP) use in healthy females is limited. The purpose(More)