The study aims to assess if a 16-week drop jump intervention from different heights shows different bone adaptations. Participants will complete four visits over a period of 16 weeks. An initial consultation will be conducted to ensure participants meet the inclusion criteria following participant recruitment. Estimated load being applied to the bone, will be assessed using non-invasive biomechanical procedures (Inertial Measurement Units, motion analysis, force plates) during drop jumps. Participants will be assigned a drop jump height of 0 cm, 30 cm or 60 cm based on a significant difference in external load at these heights or assigned to a control group where no jumps will be performed. Groups will be matched for body mass to ensure that jump height produces the load. The participants will be asked to perform 40 jumps (20 each side), 4 times per week ensuring jumping bouts are separated by 24 hours. Bone characteristics will be assessed via whole body dual-energy X-ray absorptiometry (DXA) scans and bilateral peripheral Quantitative Computed Tomography (pQCT) scans. Lab based jumping will take place on week 0, week 6, week 12, and week 16 to understand the loading applied during the different jump height groups. pQCT scans will take place on week 0, week 12, week 16 and DXA scans will take place week 0 and week 16. The reasoning of week 12 for pQCT being it may show a significant timepoint for bone formation during the remodelling cycle. During visits participants will complete a health screen, the Bone specific Physical Activity Questionnaire (BPAQ), a food frequency questionnaire and Pittsburgh sleep quality questionnaire alongside consent as tools to monitor any changes to participant lifestyle across the study. Differences in bone characteristics, lab measures and jump heights will be analysed between and within participants.

The present study aims to use varied drop jump heights to identify an osteogenic dose response effect. Drop jumps have been previously used to expose osteogenic effects in research due to the load produced at impact. Is it possible to identify an optimum height for bone response during impact? If so do we then find anything above this height actually has negative or no effect on a group of individuals?

There are few studies that attempt to identify optimal exercises for bone health with specific loading variables being quantified. The identification of an osteogenic threshold during single or multiple activity bouts would allow us to understand the optimal volume/magnitude of exercise/loading that causes an osteogenic response. Understanding the optimal exercise characteristics for osteogenesis will subsequently allow specific bone enhancing exercise to be prescribed. Currently, ambiguity exists as in the guidance for optimising bone health through exercise, for example, a recently published position statement on increasing peak bone mass in adolescents recommends that 5-6 months of vigorous physical activity should be performed but does not quantify the specific speed or intensity of activity required.

pQCT and DXA will be used to measure bone characteristics. Both methods are a common way of obtaining data detailing bone architecture and geometry within established research establishments including universities and National Health Service (NHS) trusts. Through pQCT, bone geometry, both cortical and trabecular bone can be measured and as a result, bone quality can be assessed. Bone measurement via pQCT is widely used in research and is a non-invasive method of imaging bone to provide estimates of bone strength in the peripheral skeleton to differentiate cortical from trabecular bone and assess bone geometry and density. DXA is the gold standard method of measuring bone mineral density and is commonly used to assess osteoporosis risk.

In addition, body composition (which will be derived from the DXA) may be associated with bone characteristics due to body mass and composition relating to bone loading and muscle acting on bone to produce bone strain.

Inclusion Criteria:

• 18 to 25 years old
• Have a low physical activity status defined as partaking in physical training activities no more than 2x per week.
• No current regular participation (more than once per week) in exercise programmes known to influence bone inc. gymnastics, dance, court sports, ball sports or racquet sports.
• Be able to travel to the laboratory using a vehicle or public transport
• Have the ability to comprehend and understand communication and instruction in English in order to consent and safely participate in study.
• Have no current unresolved cardiovascular complaints to avoid any cardiovascular complications when performing activities of daily living.

Exclusion Criteria:

• Prescribed medication that influences bone metabolism such as corticosteroids, anticancer drugs, and diabetes related Drugs
• Joint replacement or prostheses
• Currently or recently injured
• Medical conditions adversely affected by exposure to ionising radiation.
• History of high levels of ionising radiation exposure (e.g., medical treatment).
• Breastfeeding women, pregnant women and women trying to become pregnant
• Females who are on any form of contraception that may influence changes in bone
• Females who have current or previous history of an endocrine disorder