Horse racing is a weight category sport. One of the key challenges facing jockeys is the pressure of “making weight” throughout the protracted racing season. Aim: The aim of this study was to examine the effect of a chronically weight restrictive lifestyle and acute weight loss practices on aspects of physiological, osteogenic, metabolic and cognitive function in jockeys. Methods: The primary aim was achieved through the completion of four related studies. Study One: The effect of a 4% reduction in body mass in 48 hours on physiological and cognitive function was assessed through performance on an incremental cycle ergometer test to volitional exhaustion and a computer based cognitive test battery. Study Two: Bone mass was compared between jockeys (flat and national hunt), elite amateur boxers and a group of age, gender and BMI matched controls. Study Three: Bone mass, bone turnover and endocrine factors related to growth and metabolism were analysed in a group of jockeys and age, gender and BMI matched controls. Study Four: The impact of 6 months whole body vibration therapy (0.3 g and 30 Hz) on bone mass and turnover was analysed in a group of professional jockeys. Results: In study one maximal aerobic exercise performance was negatively affected following a 4% loss in body mass in 48 hours as evidenced by a reduction in peak power output achieved and an increase in submaximal cardiovascular strain. No changes to cognitive performance were identified in this study. In study two both groups of jockeys had lower bone mass at a number of sites than either the boxer or control groups. Adjustment of bone data revealed that differences in height and lean mass accounted for some of the variation between the groups, but that additional factors were present which may have impacted on bone mass in. Study three showed that bone mass was reduced and bone resorption increased in a jockey group. Elevated SHBG and reduced IGF-1 levels in comparison to an age, gender and BMI matched control group appeared to have a role to play in this finding. No aspect of body composition, bone mass or turnover was affected by the vibration therapy protocol used within study four. Conclusion: Results from this research appeared to indicate that aspects of physiological, osteogenic and metabolic function are affected in jockeys. This is likely to have occurred in response to a chronically weight restricted lifestyle. These findings may convey both long and short term health risks to jockeys and as such represent a major health and safety concern to the racing industry.