The test
The side plank
Sideways trunk endurance, and more usefully whether one side is much weaker than the other. It is the one test in the battery where you are compared with yourself rather than with anybody else.
What you need. A mat or carpet.
How to do it
Doing it properly
- Lie on your side, elbow under your shoulder, legs straight, top foot in front of the bottom one.
- Lift your hips so your body makes a straight line.
- Hold until you cannot maintain the line. Record the time.
- Repeat on the other side.
What stops the clock
The clock stops when your hips drop and you cannot lift them back. Both sides are recorded.
What most people get wrong
- Letting the hips sag gradually rather than stopping.
- Resting on the shoulder rather than holding through the trunk.
- Doing the second side without a proper rest.
The evidence
What it actually shows
Both sides are timed, and what is scored is the ratio between them. Two equal sides score 100. The clock stops when your hips drop and you cannot lift them back.
Scoring an asymmetry needs no normative data at all, which is its advantage: there is no reference population to be the wrong match for, because the reference is your other side. That is why this test is scored while the absolute hold times are not.
The right-to-left ratio comes from McGill's work on trunk endurance, where the balance between sides is treated as the finding rather than the duration.
The ten per cent threshold is ours and it is provisional. It comes from the Evolution pilot rather than from a paper, and it is labelled that way wherever it appears.
Published hold times come from young adults and do not transfer well across ages, so your absolute times are shown as context and marked provisional. Do not read them as a percentile, because they are not one.
An asymmetry tells you the sides differ. It does not tell you why, and it is not a diagnosis of anything.
McGill SM, right-to-left trunk endurance ratio.
Absolute durations: Evolution pilot, provisional.
The next step
One test is one test.
This measures one thing. The Evolution Index measures nine, across the three domains that decide how long you stay useful, and reports your weakest rather than your average — a strong heart does not buy you out of a floor you cannot get up from.
Every score is published with the error around it, because a change smaller than the measurement error is not a change.