The aim of this study was to investigate counter-movement jump performance and its reliability in children and adolescents with respect to age, sex and activity level. We tested 1835 children and adolescents aged between 4 and 17 years. All participants performed three counter-movement jumps on a force platform with arms akimbo. The participants were divided into six age groups and subdivided by sex within each group, to analyse age and sex effects. Subsequently, jumping performance of active and sedentary participants was compared. Jump height was calculated and the highest jump out of three was used for the calculations of peak force and peak rate of force development. Variability of all parameters was quantified using the coefficient of variation over all jumps. Jump height increased significantly with increasing age while peak rate of force development decreased. Peak force was similar for all age groups. Jump height was significantly higher in male participants and peak force and peak rate of force development was significantly lower in male participants. Variability of jump height and peak force decreased significantly with increasing age leading to reliable data above the age of 10 years. Peak rate of force development showed a high variability and, therefore, should be interpreted with caution. This could be useful information for coaches as they need to know from which age onwards the counter-movement jump is applicable in performance diagnostics and which parameters are sensible for interpretation. Finally, the present study provides data to be used as normative references.

Intermanual transfer, i.e., generalization of motor learning across hands, is a well-accepted phenomenon of motor learning. Yet, there are open questions regarding the characteristics of this transfer, particularly the intermanual transfer of dynamic learning. In this study, we investigated intermanual transfer in a force field adaptation task concerning the direction and the coordinate frame of transfer as well as the influence of a 24-h consolidation period on the transfer. We tested 48 healthy human subjects for transfer from dominant to nondominant hand, and vice versa. We considered two features of transfer. First, we examined transfer to the untrained hand using force channel trials that suppress error feedback and learning mechanisms to assess intermanual transfer in the form of a practice-dependent bias. Second, we considered transfer by exposing the subjects to the force field with the untrained hand to check for faster learning of the dynamics (interlimb savings). Half of the subjects were tested for transfer immediately after adaptation, whereas the other half were tested after a 24-h consolidation period. Our results showed intermanual transfer both from dominant to nondominant hand and vice versa in extrinsic coordinates. After the consolidation period, transfer effects were weakened. Moreover, the transfer effects were negligible compared with the subjects' ability to rapidly adapt to the force field condition. We conclude that intermanual transfer is a bidirectional phenomenon that vanishes with time. However, the ability to transfer motor learning seems to play a minor role compared with the rapid adaptation processes.

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Force field studies are a common tool to investigate motor adaptation and consolidation. Thereby, subjects usually adapt their reaching movements to force field perturbations induced by a robotic device. In this context, so-called catch trials, in which the disturbing forces are randomly turned off, are commonly used to detect after-effects of motor adaptation. However, catch trials also produce sudden large motor errors that might influence the motor adaptation and the consolidation process. Yet, the detailed influence of catch trials is far from clear. Thus, the aim of this study was to investigate the influence of catch trials on motor adaptation and consolidation in force field experiments. Therefore, 105 subjects adapted their reaching movements to robot-generated force fields. The test groups adapted their reaching movements to a force field A followed by learning a second interfering force field B before retest of A (ABA). The control groups were not exposed to force field B (AA). To examine the influence of diverse catch trial ratios, subjects received catch trials during force field adaptation with a probability of either 0, 10, 20, 30, or 40%, depending on the group. First, the results on motor adaptation revealed significant differences between the diverse catch trial ratio groups. With increasing amount of catch trials, the subjects' motor performance decreased and subjects' ability to accurately predict the force field—and therefore internal model formation—was impaired. Second, our results revealed that adapting with catch trials can influence the following consolidation process as indicated by a partial reduction to interference. Here, the optimal catch trial ratio was 30%. However, detection of consolidation seems to be biased by the applied measure of performance.

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