The skeletal and muscular systems work together as a genuine biological lever system, one of the oldest simple machines, at every single joint in the body. A joint acts as the fixed pivot point, a contracting muscle provides the pulling force, and the bone it's attached to acts as the rigid arm that force gets applied through, exactly the same three components, pivot, force and arm, that define a lever in basic mechanics.
Where a muscle attaches relative to the joint decides what the lever actually optimises for
A lever's mechanical behaviour depends heavily on where the force is applied relative to the pivot and the load, and the body's muscle attachment points follow exactly that same rule. A muscle attaching close to the joint has to contract with considerably more force to move a given load, since it's working through a short lever arm, but that short arm lets a relatively small muscle contraction produce a large, fast movement at the far end of the limb. This is exactly the trade-off, force against speed, that defines every simple lever, and the body's specific muscle attachment points represent millions of years of evolutionary tuning of that same basic trade-off for each particular joint's actual job.
Different joints are tuned toward different points along that same trade-off
A joint built mainly for fine, fast movement, like the elbow flexing the forearm, tends to have muscle attachments positioned to favour speed and range of motion over raw force, while a joint built mainly for heavy load-bearing, like the muscles stabilising the hip, tends to favour attachment points that trade some speed for considerably greater mechanical force. Comparing attachment points across different joints reveals a genuinely consistent pattern: each joint's specific lever geometry lines up closely with the actual mechanical demands of what that joint is typically asked to do, fine motor control versus heavy, sustained load-bearing.
What we're still unsure about
That joints function as biomechanical levers, and that muscle attachment points systematically trade off force against speed depending on a joint's mechanical demands, are well established principles of biomechanics, confirmed through extensive anatomical and physiological study. What's more genuinely a matter of ongoing research is exactly how precisely this lever-based framework predicts real-world injury risk and athletic performance for a given individual, since a person's specific bone lengths and exact muscle attachment points vary meaningfully between individuals, and researchers continue to study exactly how much that individual variation actually explains differences in strength, speed and injury susceptibility, rather than the basic lever model alone fully accounting for those individual differences.
This sits inside The Skeletal & Muscular Systems, one of eight topics in Human Biology, one of six domains in Biology, one of seventeen subjects the app can quiz you on.