Dr. Sam Liu | Biomechanics Professor Guy on Instagram: "For any test to be valid, we need to make sure that: It’s actually measuring what we intend to measure, not something else. It’s not confounded so obviously by other factors that render the test results ineffective. It’s logistically and practically sensible. To test overall trunk endurance, a more traditional sit up based method makes sense, or literally having the lightest counterweight makes sense. This is a trunk endurance test, not a y