Timing in Lower Limb Complex Movement Tests for DanceSport Athletes: Relation between FitLight Trainer and IMU Measurements

Abstract

We examine the relation between two devices used in measuring the timing in lower limb complex movement tests for DanceSport athletes, an inertial measurement unit (IMU) and a FitLight Trainer device, with the latter regarded as the gold standard method in the field. Four tests are selected to cover the lower limb movements. The research sample comprises 21 experienced dancers from different dance disciplines, performing the four tests with each of their lower limbs. Compared using concurrent validity, the two devices used show great agreement for estimating the total tests' run times, with interclass correlation coefficients between 0.967 and 0.994 for all tests. This agreement is additionally confirmed by Bland-Altman plots. As an alternative to other devices, the IMU sensor has proven to be a precise and suitable device for measuring timing and testing in sports. Its mobility, light weight, and size are advantages of this device in addition to measurement accuracy.

Keywords: FitLight; dance; inertial measurement unit; lower limb movements; sport; timing measurements; wearable devices.

Figure 1

(a) FitLight Trainer units positioned and fixed onto foam mat; (b) IMU sensor position and orientation on the participant’s shoe.

Figure 2

Test 1 (motion in the anterior–posterior direction): (a) starting position for right leg execution; (b) movement pattern.

Figure 3

Test 2 (motion in the medio-lateral direction): (a) starting position for the right leg execution; (b) movement pattern of the active right leg; (c) movement pattern of the active left leg.

Figure 4

Test 3 (motion following the shape of a lateral triangle): (a) starting position for the right leg execution; (b) movement pattern.

Figure 5

Test 4 (motion following the shape of a front triangle): (a) starting position for the right leg execution; (b) movement pattern of the active right leg; (c) movement pattern of the active left leg.

Figure 6

Detecting foot contact point and measuring test’s timing from the IMU acceleration signals. Magenta dots denote the detected points of contact, and in green is the successive contact point enumeration, above which the contact timings with respect to the first contact (in seconds) are also indicated.

Figure 7

Limits of agreement levels according to the Bland–Altman method for the estimated tests’ run times between FitLight Trainer and IMU device for all four tests and both active legs.