George is lifting weights. he starts by doing biceps curls which involves his elbows. his elbow is able to bend because the humero-ulnar joint is a joint. sam is doing leg presses, his knees as he pushes against the weights. the knee joint is primarily a joint, though it can act as a condylar joint when flexed. meanwhile, jane is doing "lat pulls" by pulling downward on a weighted bar. this movement involves of her arms. her shoulder joint is a joint, allowing a wide range of movements.