Primary and Secondary Levers
High Stakes Negotiations
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Every movement your body makes is a negotiation between levers — bones rotating around joints, pulling against resistance, transferring force from muscle to load. Understanding which lever is doing the primary work in any given movement is the difference between training that compounds and training that merely accumulates volume.
Identifying which body part acts as the primary lever during a given movement is simple, but "simple" isn't always obvious. Start by asking: "Which bone is being moved by the target muscle?"
During a biceps curl, the biceps pull on the forearm and flex the elbow. The forearm is the primary lever. The hand holding the weight is also a lever, but since the majority of the action occurs at the elbow rather than the wrist, the hand functions as a secondary lever. The same logic applies to a triceps extension: the triceps attach to the forearm at the elbow and produce elbow extension, making the forearm the primary lever and the hand the secondary.
The golf swing offers a clear illustration of lever hierarchy in action. The humerus is the primary lever: the shoulders drive the swing, pulling the upper arm through its arc against the resistance of the club and the ground reaction force traveling up through the body. The forearm is the secondary lever, extending at the elbow through impact to maintain the arc. The hand and wrist form the tertiary lever, the last point of force transfer before the club.
The club itself then acts as an additional lever arm, its length amplifying the force delivered at the grip into dramatically higher velocity at the clubhead. This is why wrist mechanics receive so much attention in golf instruction: a breakdown at the tertiary lever compromises everything the primary and secondary levers built upstream.
As we get into the weeds of what each lever is doing we're experiencing the concept of "simple complexity." Each individual lever is a simple construct, but when we put them together each lever is dynamically changing its relationship to every other lever, making the entire construct complex.
The Perpendicular Rule
The designation of primary, secondary, or tertiary lever depends entirely on each lever's relationship to the direction of resistance. The primary lever is always the one that passes through — or comes closest to passing through — the perpendicular line relative to that direction.
Skiing offers a clear example, specifically the action of the ski poles. At the moment of plant, the pole enters the snow roughly vertical: the tip level with the binding, the shaft close to perpendicular to the slope.
As the skier drives through the turn and passes over the plant point, the pole trails behind, and it is in that trailing phase that the forearm approaches perpendicular to the direction of resistance. That is the moment of maximum mechanical advantage, where the push through the pole delivers the most force into the stroke. Skiers who rush the pole plant and push too early, or hold too long past that perpendicular moment, are working harder than necessary for less propulsive output.
To complicate things a bit more — because by now we're all experts in simple complexity — the degree to which the forearm acts as a distinct secondary lever depends on elbow angle through the stroke.
At full elbow extension (common in high-performance technique) the arm consolidates into a single lever, and the shoulder becomes the effective pivot point. The mechanical advantage calculation then runs from shoulder to grip rather than elbow to grip, which is a longer lever arm and potentially more force delivered to the pole — provided the musculature driving the movement is functioning without inhibition through the entire chain.
Knowing where the perpendicular falls tells you which lever is primary. Knowing why it matters is a different question entirely.
