When grip strength is measured over sessions, the values should be similar if the person is giving a true maximal effort and no real change has occurred. A variation as large as 25% across a four-week interval is too big to reflect a real change in muscle capacity and more likely points to inconsistent effort during testing. Grip strength testing relies on a maximal voluntary contraction; if a person isn’t pushing maximally, the results will be lower and less reproducible from one session to the next, producing a large swing like this. Fatigue or a temporary pain flare could affect performance, but they tend to produce more uniform effects within a single testing session or follow a more predictable pattern, and an injury flare would usually show a consistent direction of change rather than a random large fluctuation. So the most plausible interpretation is that maximal effort wasn’t consistently achieved across the test-retest sessions. To improve reliability, ensure standardized testing conditions, clear encouragement, and confirm maximal effort with proper cues.