Impact Loading Effect on Bone Biomarkers in Female Runners

This study is a randomized, cross-over intervention study that will evaluate the effect of brief, high-impact loading exercises on biomarkers of bone metabolism in energy-restricted, eumenorrheic female runners. Volunteers will complete two, 5-day experimental conditions in a randomized order separated by one menstrual cycle (approximately 3 weeks). Experimental conditions will include a dietary intervention of energy intake equal to 30 kcal/kg of fat-free mass/d using controlled diets and an exercise intervention of daily treadmill running with or without an additional 50 impact loading exercises.

Many long-distance runners struggle to consume enough calories each day to match the number of calories they are burning during exercise and as part of daily living. Undereating for long periods of time is a serious concern because it can have negative effects on general health and sports performance. One of these long-term consequences is related to bone health. With undereating, bone can start to be broken down faster than it can be rebuilt. Even though it can take months, and even years, for bone to be seriously affected, this may lead to weak and brittle bones later in life, if it is left untreated. Typically, athletes are recommended to increase the number of calories they eat to prevent negative health concerns. However, not all athletes may be willing or able to increase their calories based on their performance goals, nutrition knowledge, or concerns with food security. This means that alternative strategies need to be investigated to counteract the negative effects of undereating on bone health. This study proposes to evaluate the effect of adding short bouts of high-impact jumping exercises to typical endurance training to promote healthy bone metabolism. This will specifically involve completing two phases of a supervised treadmill run and consuming a reduced-calorie diet (provided by the research team) on 5 consecutive days. In addition, one of the phases will include performing 5 sets of 10 jumping exercises on 5 consecutive days in addition to the treadmill run. Results of the study will serve as an important first step in helping exercise and medical professionals understand more about how to protect and manage the bone health of female long-distance runners.

Eligibility Criteria:
Inclusion Criteria:

* Females runners with regular menstrual cycles, not using contraceptives
* Body Mass Index between 18.5-25.0 kg/m2
* Weight stable (+/- 2 kg) for 6 months
* Running volume of ≥30 miles per week, frequency of at least 5 days per week
* VO2max of ≥45 ml/kg/min
* Willing to consume provided meals and snacks

Exclusion Criteria:

* Low Energy Availability in Females Questionnaire (LEAF-Q) score ≥8
* Menstrual disturbances measured by progesterone and self-report
* Using contraceptives (oral contraceptives, injections, intrauterine device, etc.)
* Low Bone Mineral Density (z-score \< -1)
* Routine engagement in mechanical loading exercises
* History of fracture in the previous 6 months
* Recent recovery (within the last 12 months) or still in recovery after eating disorder diagnosis
* Medication use that could affect bone metabolism (e.g., corticosteroids, anticonvulsants, heparin, gonadotropin-releasing hormone agonists)
* Pregnancy or lactation
* Abnormal thyroid-stimulating hormone levels