Reliability and validity of the GymAware optical encoder to measure displacement data

The purpose of this study was to determine the reliability and validity of the GymAware optical encoder (Kinetic, Canberra, ACT) to measure displacement data (distance, peak velocity, mean velocity and time). Three GymAware sensors were attached to a Calibration Rig (CalRIG), a novel piece of technology engineered specifically for accurate calibration of dynamometry equipment. The CalRIG was programmed to perform 4 identical sets of 14 repetitions, each repetition increasing in displacement by 0.1m and 0.2m/s. Validity of displacement measures by GymAware were evaluated by typical error estimate (TEE), intraand interreliability was assessed through typical error measurement (TEM). TEE values were very low at 0.00m for distance and 0.01m/s for mean and peak velocity variables. TEE was higher at up to 0.16s for time (repetition duration). TEM was 0.00m for distance, 0.010.02m/s for velocity and 0.01-0.02s for repetition duration variables when comparing both between sensors and between sets. In conclusion, the GymAware optical encoder accurately measured displacement of the CalRIG shaft, thereby indicating its validity as a linear position transducer employed to calculate other strength and power related variables of interest through differentiation of measured displacement data. GymAware was found to be highly reliable with little variation between sets or sensors, of great benefit to practitioners or coaches utilizing GymAware in assessment and monitoring of athletic performance over time. It is recommended that consumers use velocity as a performance indicator as the measurement of this variable showed only minor error. A Smith machine is also recommended during resistance exercises to control the direction of displacement and facilitate measurement.