RESUMEN
BACKGROUND: There is limited evidence describing the relationship between calcaneal bone mineral density (cBMD) and activity level, menstrual history, or the development of bone stress injury (BSI). HYPOTHESIS/PURPOSE: The purposes of this study were to: 1) examine the influence of physical activity on cBMD in healthy college students (HCS), 2) determine if there is an association between cBMD, body mass index (BMI), sex, menstrual history, and history of BSI in HCS, and 3) compare the cBMD of HCS to cBMD data collected on intercollegiate athletes (ICA) from a previous study. STUDY DESIGN: Cross-sectional design. METHODS: This cross-sectional study recruited a convenience sample of HCS at one institution. Subjects provided self-reported injury and menstrual history, completed a physical activity questionnaire, and cBMD and BMI measures were obtained. Descriptive statistics, statistical analyses of relationships (Chi-square and relative risk), logistic regression, and differences (t-tests) were used in the statistical analyses. RESULTS: One hundred three HCS (82 female, 21 male; age 21.9 ± 1.13) consented to participate. The composite score for work, leisure, and sport activity ranged from 5.6 to 11.1 (7.9 ± 1.1) for HCS subjects. There was no significant correlation between cBMD and physical activity in HCS, however, a significant correlation was found between reported age of onset of menstruation and left and right cBMD (r = -0.22 and r = -0.23; p < 0.05) and history of secondary amenorrhea and history of BSI (r = 0.32; p < 0.05). There was no difference in cBMD between the male ICA and male HCS, but highly significant differences in cBMD between the female ICA and female HCS groups (p < 0.000). CONCLUSIONS: Age of menarche and secondary amenorrhea are significantly associated with cBMD and history of BSI in HCS subjects, respectively. Differences in cBMD among the HCS subjects were not related to activity level. cBMD was significantly lower in female HCS as compared to female ICA. This difference in cBMD between ICA and HCS may be activity related. LEVEL OF EVIDENCE: Level 3.
RESUMEN
The purpose of this study was to evaluate the hypothesis that a novel high-repetition, low-resistance back squat training protocol, designed to stimulate high-intensity interval training, improves 5-km run performance. Fifteen runners [4 male, 11 female; 150 + minutes of endurance exercise/week; age = 22.7 ± 2.0 y; 21.5 ± 2.2 kg/m2 BMI] in this single-group test-retest design completed two weeks of back squats consisting of three sets of 15-24 repetitions at 60% of estimated one-repetition max (1RM), three times per week (1-2 days of rest between sessions). Outcome tests included a 5-km outdoor timed run, laboratory indirect calorimetry to quantify substrate oxidation rates during steady-state submaximal exercise (60% and 70% heart rate max (HRmax)), and estimated 1RM for back squats. Back squat estimated 1RM increased by 20% (58.3 ± 18.5 to 70.2 ± 16.7 kg, P < 0.001). However, 5-km run times due to the back squat protocol did not significantly change (Pre-Squats: 23.9 ± 5.0 vs. Post-Squats: 23.7 ± 4.3 minutes, P = 0.71). Likewise, the squat training program did not significantly alter carbohydrate or lipid oxidation rates during steady-state submaximal exercise at 60% or 70% of HRmax (P values ranged from 0.36 - 0.99). Short term high-repetition back squat training does not appear to impact 5-km run performance or substrate utilization during submaximal exercise.
RESUMEN
PURPOSE: The purpose of this study was to examine the relationships between isotonic ankle plantar flexor endurance (PFE), foot pronation as measured by navicular drop, and exercise-related leg pain (ERLP). BACKGROUND: Exercise-related leg pain is a common occurrence in competitive and recreational runners. The identification of factors contributing to the development of ERLP may help guide methods for the prevention and management of overuse injuries. METHODS: Seventy-seven (44 males, 33 females) competitive runners from five collegiate cross-country (XC) teams consented to participate in the study. Isotonic ankle PFE and foot pronation were measured using the standing heel-rise and navicular drop (ND) tests, respectively. Demographic information, anthropometric measurements, and ERLP history were also recorded. Subjects were then prospectively tracked for occurrence of ERLP during the 2009 intercollegiate cross-country season. Multivariate logistic regression analysis was used to examine the relationships between isotonic ankle joint PFE and ND and the occurrence of ERLP. RESULTS: While no significant differences were identified for isotonic ankle PFE between groups of collegiate XC runners with and without ERLP, runners with a ND >10 mm were almost 7 times (OR=6.6, 95% CI=1.2-38.0) more likely to incur medial ERLP than runners with ND <10 mm. Runners with a history of ERLP in the month previous to the start of the XC season were 12 times (OR=12.3, 95% CI=3.1-48.9) more likely to develop an in-season occurrence of ERLP. CONCLUSION: While PFE did not appear to be a risk factor in the development of ERLP in this group of collegiate XC runners, those with a ND greater than 10 mm may be at greater odds of incurring medial ERLP. LEVEL OF EVIDENCE: 2b.
