Grant: Discovery Grants Program - Individual

Cycling is a popular activity however since it is `low impact', cycling predominantly benefits the cardiovascular system, rather than having an impact on the skeleton. In contrast, a `high impact' (i.e., weight bearing) activity, such as running, would also cause large external forces to be applied to the skeleton. One of the benefits of such forces is that they can stimulate bone metabolism, and in turn improve bone density. Beyond these mechanics, there are also other conditions within the sport of cycling that can affect bone integrity over time, including low intake of energy via food/drink, reduced daily weight bearing loads due to long hours spent cycling, weight loss, as well as excess calcium losses through sweat and urine. We do not yet understand the specific effects of each of these factors on the metabolic processes of bone, which leads to the question of whether it is the low-impact, non-weight bearing nature of cycling, which extends to other forms of low-impact activities (e.g., swimming), or other conditions that have a seemingly negative impact on bone. In this series of studies, we aim to use cycling as a model to better understand the detrimental effects of low-impact exercise on the processes that lead to changes in bone metabolism, including energy availability (i.e., adequate dietary intake), cycling duration, time-of-day, markers of inflammation, and the effects of oral contraceptives. Three cross-over studies will be conducted, where young, non-cyclist adults will perform all experimental conditions in random order. In each study, blood will be collected before and following either a single bout of cycling or a short period of cycling training and will be tested for changes in blood markers that reflect bone metabolism and inflammation. Study 1 will investigate the effects of three cycling durations (30, 60, and 120 min) on bone metabolism and inflammation in male and female adults who have eaten adequate calories. Study 2 will explore the effects of time-of-day (morning vs evening) on markers of bone metabolism and inflammation after two different types of exercise: low impact (cycling) and high impact (running) in male and female adults who have eaten adequate calories for their exercise session. Study 3 will explore the effects of dietary energy restriction during one week of cycling training on the processes involved in bone metabolism. At the same time, we will explore whether taking oral contraceptives (birth control pills) can alter any of these effects. Only females will participate in this study and their diet will be prescribed during both cycling weeks such that on one condition they would have consume adequate calories and on a second condition their diet would be restricted to 20% less calories. This series of studies is the first of its kind and the findings will used to better understand bone tissue growth, development, and adaptations that can take place in response to alterations in diet and exercise.