Deborah L. King

An algorithm for determining gravity line location from posturographic recordings

In posturographic recordings, the center of pressure (COP) displacement does not accurately reflect migration of the gravity line (GL), the vertical line passing through the bodys center of gravity, COG. Since the horizontal ground reaction force, Fx, is proportional to the horizontal acceleration of the COG its second integral does represent the horizontal position of the gravity line (GLP). However, the initial constants of integration, initial velocity and position, are not known. In this note, a technique for estimating these integration constants is suggested: zero-point-to-zero-point integration. This method is based on a postulation that when Fx = 0, the GLP and COP coincide. By integrating Fx from one zero point to another zero point, both the instantaneous GLP and its velocity are determined. A validation of the suggested algorithm was performed using optical methods to determine the GLP during a one legged standing tasks. Cross-correlation values of GLP determined via videography and the suggested algorithm ranged from 0.79 to 0.96. These results suggest that the zero-point-to-zero-point-integration is an acceptable technique for determining GLP from posturographic recordings.

Optimizing power output by varying repetition tempo.

Pryor, RR, Sforzo, GA, and King, DL. Optimizing power output by varying repetition tempo. J Strength Cond Res 25(11): 3029–3034, 2011—The effects of varying interrepetition rest and eccentric velocity on power output (PO) and the number of repetitions performed during a bench press set were examined in 24 college-aged resistance trained men. On 6 separate occasions, subjects performed a set of bench press at 80% 1 repetition maximum until volitional fatigue. For each of the 6 repetition tempo trials, the bench press set was paced by metronome to a unique repetition tempo involving a combination of the following: interrepetition rest of 0 or 4 seconds; eccentric velocity of 1 or 4 seconds and bottom rest of 0 or 3 seconds. The velocity of concentric contraction was maximal during all 6 tempo trials. During each trial, video data were captured to determine PO variables and number of successful repetitions completed at each tempo. One-way repeated measures analysis of variance showed tempos with a fast eccentric phase (1 second), and no bottom rest produced significantly greater (p ≤ 0.05) PO and repetitions than tempos involving slower eccentric velocity (4 seconds) or greater bottom rest (4 seconds). This combination of greater repetitions and PO resulted in a greater volume of work. Varying interrepetition rest (1 or 4 seconds) did not significantly affect PO or repetitions. The results of this study support the use of fast eccentric speed and no bottom rest during acute performance testing to maximize PO and number of repetitions during a set of bench press.

Validity and Intra-rater Reliability of 2-Dimensional Motion Analysis Using a Hand-held Tablet Compared to Traditional 3-Dimensional Motion Analysis.

CONTENT Lower extremity landing mechanics have been implicated as a contributing factor in knee pain and injury, yet cost effective and clinically accessible methods for evaluating movement mechanics are limited. The identification of valid, reliable, and readily accessible technology to assess lower extremity alignment could be an important tool for clinicians, coaches, and strength and conditioning specialists. OBJECTIVE The purpose of this study was to examine the validity and reliability of using a hand-held tablet and movement analysis application (app) for assessing lower extremity alignment during a drop vertical jump task. DESIGN Concurrent Validation. SETTING Laboratory. PARTICIPANTS Twenty-two healthy college aged subjects (11 female and 11 male, mean age = 21 ± 1.4 years; mean height: 1.73 ± .12 m, mean mass: 71 ± 13 kg) with no lower extremity pathology that prevented safe landing from a drop jump. INTERVENTION Subjects performed six drop vertical jumps which were recorded simultaneously using a 3D motion capture system and a hand-held tablet. MAIN OUTCOME MEASURES Angles on the tablet were calculated using a motion analysis app and from the 3D motion capture system using Visual 3D. Hip and knee angles were measured and compared between both systems. RESULTS Significant correlations between the tablet and 3D measures for select frontal and sagittal plane ranges of motion (ROM) and angles at maximum knee flexion (MKF) ranged from r = 0.48 (P = .036) for frontal plane knee angle at MKF to r = .77 (P<.001) for knee flexion at MKF. CONCLUSION Results of this study suggest that a hand-held tablet and app may be a reliable method for assessing select lower extremity joint alignments during drop vertical jumps, but this technology should not be used to measure absolute joint angles. However, sports medicine specialists could use a hand-held tablet to reliably record and evaluate lower extremity movement patterns on the field or in the clinic.

Instrumented figure skating blade for measuring on-ice skating forces

Competitive figure?skaters experience substantial, repeated impact loading during jumps and landings. Although these loads, which are thought to be as high as six times body weight, can lead to overuse injuries, it is not currently possible to measure these forces on-ice. Consequently, efforts to improve safety for skaters are significantly limited. Here we present the development of an instrumented figure?skating blade for measuring forces on-ice. The measurement system consists of strain gauges attached to the blade, Wheatstone bridge circuit boards, and a data acquisition device. The system is capable of measuring forces in the vertical and horizontal directions (inferior?superior and anterior?posterior directions, respectively) in each stanchion with a sampling rate of at least 1000?Hz and a resolution of approximately one-tenth of body weight. The entire system weighs 142?g and fits in the space under the boot. Calibration between applied and measured force showed excellent agreement (R?>?0.99), and a preliminary validation against a force plate showed good predictive ability overall (R???0.81 in vertical direction). The system overestimated the magnitude of the first and second impact peaks but detected their timing with high accuracy compared to the force plate.

Reliability of Using a Handheld Tablet and Application to Measure Lower-Extremity Alignment Angles

CONTEXT Landing kinematics have been identified as a risk factor for knee injury. Detecting atypical kinematics in clinical settings is important for identifying individuals at risk for these injuries. OBJECTIVE To determine the reliability of a handheld tablet and application (app) for measuring lower-extremity kinematics during drop vertical-jump landings. DESIGN Measurement reliability. SETTING Laboratory. PARTICIPANTS 23 healthy young adults with no lower-extremity injuries and no contraindications for jumping and landing. INTERVENTION Subjects performed 6 drop vertical jumps that were captured with an iPad2 and analyzed with a KinesioCapture app by 2 novice and 2 experienced raters. Three trials each were captured in the frontal and sagittal planes. MAIN OUTCOME MEASURES Frontal-plane projection angles, knee flexion, and hip flexion at initial contact and maximum knee flexion were measured. ICC and SEM were calculated to determine intertrial and interrater reliability. One-way ANOVAs were used to examine differences between the measured angles of the raters. RESULTS Average intertrial reliability ranged from .71 to .98 for novice raters and .77 to .99 for experienced raters. SEMs were 2.3-4.3° for novice raters and 1.6-3.9° for experienced raters. Interrater ICC2,1 was.39-.98 for the novice raters and .69-.93 for the experienced raters. SEMs were smallest with the experiences raters, all less than 1.5°. CONCLUSION A handheld tablet and app is promising for evaluating landing kinematics and identifying individuals at risk for knee injury in a clinical setting. Intertrial reliability is good to excellent when using average trial measures. Interrater reliability is fair to excellent depending on experience level. Multiple trials should be assessed by a single rater when assessing lower-extremity mechanics with a handheld tablet and app, and results may vary with experience level or training.