Summary
This quote suggests that someone, in this case, Shearer, may be at a high level of physical fitness but not at their absolute best or optimal level of fitness. While they may be in good shape, they may still have room for improvement or might be lacking certain key elements that would define peak fitness. In other words, being at 100% fitness implies being healthy and fit overall, but true peak fitness goes beyond that and entails reaching an exceptional level of performance and physical condition.