Effect of acute fatigue on force generation accuracy and repeatability in youth athletes

The study aimed to evaluate the acute effect of the incremental running test on the accuracy and repeatability of submaximal force generation in adolescent athletes (biathletes and runners) with different training regimes. The isometric force generation was assessed in biathletes and runners by examining left and right elbow extension (LEE; REE); flexion (LEF; REF); left and right knee extensions (LKE; RKE) before and after the test. The mean force of 10 sub-maximal targeted force pulses (Fmean) and force variability parameters: standard deviation and coefficient variation were used for accuracy and repeatability estimation. Biathletes generated forces more accurate and exhibit better repeatability of produced forces than runners. Mean force measured in fatigue conditions, for both groups, did not vary significantly from rest measurements. Before testing biathletes exhibited significantly lower REE and LEE, and after testing lower REF and LEF variability than runners. After testing there was a significant drop of variability in elbows flexion but not extension and RKE in biathletes. Insignificant downward trend of variability parameters were found in runners. The presented findings corroborate sport-specific force generation ability alteration in response to exhaustive effort. Tracking force generation over time may be useful in the monitoring of training loads and specific training adaptations.

Effects of Different Forms of Extrinsic Feedback on the Accuracy of Force Production and to Differentiate this Force in the Simple Cyclic Movements of the Upper and Lower Limb

Background: This study aimed to assess the accuracy of force production by the limbs and to identify the ability to differentiate this force during a progressively increasing value, in response to different types of extrinsic feedback.

Material and methods: The study involved nineteen healthy and physically active boys and girls aged 12.82±0.34 years, body height 157.05±9.02 cm, and body mass 44.89±7.89 kg. The tasks were to perform a series of right and left upper limb pulls and pushes with increasing force using the levers of the kinesthesiometer and a series of lower limb presses on the pedal of the kinesthesiometer. The tasks were completed in three feedback conditions: no feedback, sound feedback, verbal feedback, and the retention test was used. To assess the level of accuracy of force production, the novel index of force production accuracy (FPAIndex) was used.

Results: The outcomes expressing the value of FPAIndex on the point scale indicated that the highest level of kinesthetic differentiation was observed when no feedback was provided (1.17 points), and the lowest kinesthetic differentiation was recorded when verbal feedback was provided (3.33 points). However, they were devoid of statistical value. The repeated-measures analysis of variance ANOVA with the Tukey post-hoc test (HSD) indicated a significant lowest (p=0.0402) level of accuracy of FPA (x̄ 36.12±18.29 [N]) only for the act of left lower limb press (LL PRESS) in the retention test, while no feedback was provided to the subjects.

Conclusions: The results of this study showed that verbal and sound extrinsic feedback did not affect the accuracy of force production by the upper and lower limbs and the ability to differentiate this force in simple movements among children.