Results

Introduction

Methods

Modern strength training facilities often employ various types of external dynamometers to determine barbell velocity and power. By utilizing these devices training programs can be correctly implemented to maximize performance of athletes regardless their current level of physical preparedness for a given workout. However, these external dynamometers vary greatly on their accuracy and ease of use.

A half-rack free weight lifting station was outfitted with two overhead mounted 3-D video cameras sampling at 30 Hz, interfaced with a self-contained computer and software system, and operated with a touch screen (EliteForm, Lincoln, NE). For comparison purposes, a 3’x8’ uni-axial force plate (Rough Deck, Rice Lake, WI) was placed directly under the half-rack, and a ceiling–mounted linear position transducer (Unimeasure, Corvallis, OR) was attached via a tether to the barbell. Data from the force plate and position transducer were sampled at 1000 Hz using a BioPac data acquisition system (Goleta, CA). Velocity (m.s-1) and power (W) were derived using LabView software (National Instruments, Austin, TX). One weight-trained male subject (age = 28 yrs, hgt. = 1.78 m, wgt. = 97.1 kg, barbell squat 1 repetition maximum [1 RM] = 226.8 kg) performed parallel high-bar back squats for 10 sets x 1 repetition at 30, 40, 50, 60, 70 and 80% 1 RM loads using maximal acceleration

Lab-derived dependent variables were as follows; PP = 2755.1520.5 W, MP = 1550.2338.5 W, PV = 1.3460.423 m.s-1, MV = 0.7620.264 m.s-1. Correlation coefficients for all dependent variables ranges from r = 0.94 – 0.99, while regression slopes were all comparable to 1.0 (b = 0.88 – 1.05). No significant differences between testing devices were observed for any variable. SEE were as follows; PP = 110.9 W, MP = 28.3 W, PV = 0.069 m.s-1, and MV = 0.016 m.s-1. Figures 1, 2, 3, and 4 show the scatter plots for each of the variables. Table 1 lists each of the variables in greater detail for t scores, r (correlations), b terms (slope), SEE, and relative standard errors.

M.T. Lane, A.C. Fry, T.J. Herda, A. Hudy, M. Cooper, M.J. Andre, J. Weir, J. Siedlik, Z. Graham and W. Hawkins. Biomechanics Laboratory, Dept. of Health, Sport & Exercise Sciences, University of Kansas,

Lawrence, KS

DISCUSSION

These data support the use of the 3-D video motion capture system for assessing power and velocity during free weight resistance exercise. Not only were the values obtained from both testing modalities similar, their relationships with each other were extremely high. Finally, the SEE clearly indicate that the expected errors when using the 3-D video motion capture system were well within acceptable ranges when considering the magnitude of the variables measured in the present study.

PurposeTo determine the validity of kinetic and kinematic data obtained using a 3-dimensional (3-D) video motion capture system during resistance exercise

This project was supported in part by EliteForm LLC & Nebraska Global LLC

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VALIDATION OF A 3-DIMENSIONAL VIDEO MOTION CAPTURE SYSTEM FOR DETERMINING WEIGHT TRAINING KINETICS AND KINEMATICS

Figure 1 – Peak power (W) comparison

Axis A – Force plate & position transducer. Axis B – EliteForm.Figure 2 – Mean power (W) comparison.

Axis A – Force plate & position transducer. Axis B – EliteForm.

Figure 3 – Peak velocity (m.s-1) comparison.

Axis A – Force plate & position transducer. Axis B – EliteForm.Figure 4 – Mean velocity (m.s-1) comparison.

Axis A – Force plate & position transducer. Axis B – EliteForm.

________________________________________________________________________________________________ Variable Lab EliteForm t r b- SEE % error

X±SD X±SD term (SEE/Lab mean)________________________________________________________________________________________________ Peak Power (W) 2755.1± 2770.2± 0.1532 0.944 0.8805 110.9 4.0%

520.5 554.0 Mean Power (W) 1550.2± 1447.6± 1.7059 0.993 0.8898 28.3 1.8%

338.5 308.6 Peak Velocity 1.346± 1.393± 0.5498 0.990 1.0456 0.069 5.1% (m.s-1) 0.423 0.448 Mean Velocity 0.762± 0.746± 0.3438 0.998 0.9842 0.016 2.1% (m.s-1) 0.264 0.260________________________________________________________________________________________________ *t-test; α<.00625 using Bonferroni correction (note: no comparisons were significantly different).

Photos – Subject performing squats (left), dual 3-D video cameral motion capture system mounted on half-rack lifting station (left & above), touch screen control panel for experimental motion capture system (right).

during the concentric phase. Dependent variables included peak (PP) and mean power (MP) and peak (PV) and mean velocity (MV). Linear regressions between lab-derived and 3-D video-derived data provided correlation coefficients, regression slopes (b), and standard errors of estimate (SEE). Data (XSD) for each testing system were compared using independent t-tests with Bonferroni corrections (p ≤ 0.00625)