Are change of direction speed and agility different abilities from time and coordinative perspectives?

This study aimed to test whether agility and change of direction speed (COD) are independent capacities using the same movement pattern (1) in terms of the completion time and (2) the entropy. Seventeen semi-professional female football players participated in the study. The agility task consisted of a Y-shaped (45° COD) task with three possible exit options (center, right and left) performed pre-planned or in reaction to the movement of two testers (i.e., blocking exit gates). Players' acceleration was measured using an inertial measurement unit. Entropy was calculated from the acceleration signal and completion time was extracted using a magnet-based timing system. Significantly greater times and lower entropy (p<0.001) were found during agility runs to pre-planned COD runs. Furthermore, weak to moderate correlations were found between COD and agility for both completion time (r = 0.29, p<0.001) and entropy (r = 0.53, p<0.001, r2 = 28.1%). These results highlight that COD speed and agility are independent capacities and skills, and as such, should be tested and trained as distinct, separate qualities. Modifying task constraints including a reactive stimulus (i.e., cognitive factors), is essential for increasing task complexity by altering the biomechanical and coordinative aspects of the action.

Adding mechanical vibration to a half squat with different ballasts and rhythms increases movement variability.

The aim of this study was to determine whether whole body vibration increases movement variability while performing a half squat with different ballasts and rhythms through entropy. A total of 12 male athletes (age: 21.24 ± 2.35 years, height: 176.83 ± 5.80 cm, body mass: 70.63 ± 8.58 kg) performed a half squat with weighted vest, dumbbells and bar with weights suspended with elastic bands, with and without vibration at the squat rhythm of 40 and 60 bpm. Each ballast corresponded to 15% of the body mass. The movement variability was analysed by calculating the sample entropy of the acceleration signal, recorded at the waist using an accelerometer. With vibration, differences were found between weighted vest and dumbbells (t(121) = -8.81, p < 0.001 at 40 bpm; t(121) = -8.18, p < 0.001 at 60 bpm) and between weighted vest and bar at both rhythms (t(121) = -8.96, p < 0.001 at 40 bpm; t(121) = -8.83, p < 0.001 at 60 bpm). Furthermore, a higher sample entropy was obtained at 40 bpm with all ballasts (t(121) = 5.65, p < 0.001 with weighted vest; t(121) = 6.27, p < 0.001 with dumbbells; t(121) = 5.78, p < 0.001 with bar). No differences were found without vibration. These findings reveal that adding mechanical vibration to a half squat produces a non-proportional increase in movement variability, being larger when the ballast is placed on the upper limbs and when performed at a slow rhythm.

Assessing the Reliability and Validity of Agility Testing in Team Sports: A Systematic Review.

ABSTRACT: Yepes, MM, Feliu, GM, Bishop, C, and Gonzalo-Skok, O. Assessing the reliability and validity of agility testing in team sports: A systematic review. J Strength Cond Res 36(7): 2035-2049, 2022-The aims of this systematic review were to (a) examine the reliability of the reactive agility tests and (b) analyze the discriminatory validity of the agility tests. A literature search was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We explored PubMed, SPORTDiscus, and Cochrane Plus databases looking for articles about agility in team sports. After filtering for article relevance, only 42 studies met the inclusion criteria; 37 of which assessed the reliability of agility tests and 22 assessing their validity. Reliability showed a high intraclass correlation coefficient (ICC) in almost all studies (range 0.79-0.99) with the exception of 2 studies. In addition, other studies also assessed the reliability of decision time (ICC = 0.95), movement time (ICC = 0.92), and decision accuracy (ICC = 0.74-0.93), all of which exhibited acceptable reliability. Furthermore, these data show high discriminatory validity, with higher performance level players being faster than lower performance level players (mean = 6.4%, range = 2.1-25.3%), with a faster decision time (mean = 23.2%, range = 10.2-48.0%) with the exception of 1 study, and better decision accuracy (mean = 9.3%, range = 2.5-21.0%). Thus, it can be concluded that reactive agility tests show good reliability and discriminatory validity. However, most agility tests occur in simple contexts whereby only 2 possible responses are possible. Therefore, future research should consider creating more specific and complex environments that challenge the cognitive process of high-level athletes.

Validity of a Magnet-Based Timing System Using the Magnetometer Built into an IMU.

Inertial measurement units (IMUs) represent a technology that is booming in sports right now. The aim of this study was to evaluate the validity of a new application on the use of these wearable sensors, specifically to evaluate a magnet-based timing system (M-BTS) for timing short-duration sports actions using the magnetometer built into an IMU in different sporting contexts. Forty-eight athletes (22.7 ± 3.3 years, 72.2 ± 10.3 kg, 176.9 ± 8.5 cm) and eight skiers (17.4 ± 0.8 years, 176.4 ± 4.9 cm, 67.7 ± 2.0 kg) performed a 60-m linear sprint running test and a ski slalom, respectively. The M-BTS consisted of placing several magnets along the course in both contexts. The magnetometer built into the IMU detected the peak-shaped magnetic field when passing near the magnets at a certain speed. The time between peaks was calculated. The system was validated with photocells. The 95% error intervals for the total times were less than 0.077 s for the running test and 0.050 s for the ski slalom. With the M-BTS, future studies could select and cut the signals belonging to the other sensors that are integrated in the IMU, such as the accelerometer and the gyroscope.