The influence of sample and filter frequencies on baseball pitching data

Area of Science:

• Biomechanics
• Sports Science
• Motion Analysis

Background:

• Baseball pitching is the fastest human motion, requiring high sample frequencies for accurate data capture.
• Previous research utilized varying sample frequencies (240-500 Hz) and low-pass filter frequencies (commonly 13.4 and 18.0 Hz).

Purpose of the Study:

• To investigate the impact of different sample frequencies (240 Hz and 480 Hz) and low-pass filter frequencies (13.4 Hz, 18.0 Hz, 27.2 Hz) on baseball pitching biomechanics.
• To determine which frequency parameter, sample or filter, has a greater influence on kinematic, temporal, and kinetic variables.

Main Methods:

• Collected marker-based motion capture data of fastballs from 28 professional pitchers at 480 Hz.
• Down-sampled data to 240 Hz and applied three low-pass filter frequencies (13.4, 18.0, 27.2 Hz) to each dataset.
• Computed 26 biomechanical variables and compared differences using two-way repeated measures ANOVA, referencing minimal clinically important differences (MCID).

Main Results:

• Filter frequency demonstrated a greater impact, causing significant differences above MCID in 13 of 26 variables, compared to sample frequency (4 of 26 variables).
• Variables requiring differentiation, such as velocities and torques, were most affected by frequency choices.
• Differences were interpreted relative to minimal clinically important differences (MCID).

Conclusions:

• A minimum sample frequency of 240 Hz is recommended for marker-based motion capture in pitching analysis.
• A Butterworth low-pass filter frequency of 18.0 Hz is suggested for optimal accuracy in capturing pitching mechanics.
• Filter frequency is a more critical parameter than sample frequency for analyzing pitching biomechanics.