Belt rank greatly represents proficiency. The punch form and consistency, the objectively more significant of the three research objectives, were correlated with each other. Peak punch velocity is directly related to punch impact, but the impulse (impact) of a punch is also influenced by the mass of the moving object. 

Correct punching form ensures maximal mass behind a punch, and consistency and form both prevent injury in execution. Therefore, the result that there was no correlation between peak punch velocity and belt rank or years of training is not as significant as the findings in the first two research objectives.

This video explains each of the limitations below.

Sample size - There were few participants, so there was no way to obtain statistically significant data. Ideally, there would be multiple participants for each belt rank trained for a different number of years and from trained at different schools under the same discipline. This would eliminate the most prominent confounding variables.

Generated criteria - The criteria used to quantify adherence to form is not technically a verified method of "grading" form; computer algorithms and AI, while not accessible, would have produced more accurate results.

Rotational aspect - Because videography was performed through one plane of motion, there was a possible inaccuracy in measuring the displacement, and consequently velocity, of each punch. If there was a second camera angle from the top looking down at the participant punching, the depth of the moving arm would give more accurate data.

Verification of a Belt System (explained above as conclusion)

Use of form criteria - The use of generated criteria from Ishac & Eager in this study guided the evaluation of punching form. Because this was successful, further research could compare criteria point systems to computer generated algorithms. Amateur martial artists without access to coaching, punch trackers, or algorithms could instead use criteria for self-improvement.