BACKGROUND:Closed kinetic chain and plyometric exercises are commonly used in aquatic rehabilitation because they are believed to reduce joint loading whilst replicating functional tasks. However, the forces and relationship to land-based functional movement is unknown. This study aims to compare vertical ground reaction force during squats, calf raises and jumping in older adults with and without knee osteoarthritis on land and in water. METHODS:Forty one participants (Healthy n = 21; Knee osteoarthritis n = 20; Age 68.5 (4.4) years) completed squats and calf raises at slow, medium and maximal speeds and jumping at maximal speed on land and in waist and chest depth water. Vertical ground reaction force and pain rating was measured in each environment. RESULTS:Force in all exercises was significantly greater on land than in chest depth water (p < 0.005). Peak force was significantly greater at maximal speed compared to slow speed (p < 0.001). The pattern of force in squats at slow speed in water was different to on land, with force highest at the start and end of the exercise and decreasing in the central phase. Pain ratings were significantly lower (p < 0.001) in water compared to on land in squats. CONCLUSIONS:Closed kinetic chain exercises offer inherently different loading in an aquatic environment. Body weight squats and calf raises in water could be defined as either neuromotor or low load, high velocity training. Maximal speed exercise in water produces higher relative load compared to slow speed and minimal pain providing an opportunity for clinicians to use greater speed to address power deficits.