Inter-limb coordination dynamics: effects of visual constraints and age

This study aimed to verify the effect of visual afference (eyes open – EO vs. eyes closed – EC) on inphase (IP) and anti-phase (AP) homolateral inter-limb coordination performance in relation to age. Forty individuals (12 youths, age=12±1 years; 16 young adults, age=24±3 years; 12 older adults, age=59±11 years) performed IP and AP synchronized (80, 120, and 180 bpm) hand and foot flexions and extensions. Variability of IP and AP movements was obtained by calculating the within-subject standard deviation of each condition. Significant interactions between coordination mode × age and coordination mode × age × visual afference showed joint effects on IP and AP variability, while no main effects emerged. In the IP-EO condition, posthoc analysis showed higher (p=.0003) variability in older adults (24.8±6.6 s) with respect to young adults (10.5±10.9 s), whereas in the IP-EC condition, older adults showed higher (p=.03) variability (23.4±10.7 s) with respect to both youths (13.7±8.6 s) and young adults (24.1±12.2 s). In both AP conditions, older adults showed lower (p<.002) variability values (EO=9.5±12.1 s; EC=4.6±7.5 s) with respect to the other age groups, with only the youth group showing differences between EO (16.6±12.1 s) and EC (23.6±8.4 s) conditions. Findings show that the age-related worsening of inter-limb coordination is independent of the use of visual afferences. In contrast, at developmental age, visual perception seems to play a differential role depending on the coordinative task complexity (IP/AP). It becomes crucial only in the AP condition, with a lower variability in the EO than in the EC condition indicating youths’ tendency to rely more on visual information for stabilizing complex inter-limb coordination performance

Usefulness of Linear Mixed-Effects Models to Assess the Relationship between Objective and Subjective Internal Load in Team Sports

Internal load can be objectively measured by heart rate-based models, such as Edwards' summated heart rate zones, or subjectively by session rating of perceived exertion. The relationship between internal loads assessed via heart rate-based models and session rating of perceived exertion is usually studied through simple correlations, although the Linear Mixed Model could represent a more appropriate statistical procedure to deal with intrasubject variability. This study aimed to compare conventional correlations and the Linear Mixed Model to assess the relationships between objective and subjective measures of internal load in team sports. Thirteen male youth beach handball players (15.9 ± 0.3 years) were monitored (14 training sessions; 7 official matches). Correlation coefficients were used to correlate the objective and subjective internal load. The Linear Mixed Model was used to model the relationship between objective and subjective measures of internal load data by considering each player individual response as random effect. Random intercepts were used and then random slopes were added. The likelihood-ratio test was used to compare statistical models. The correlation coefficient for the overall relationship between the objective and subjective internal data was very large (r = 0.74; ρ = 0.78). The Linear Mixed Model using both random slopes and random intercepts better explained (p < 0.001) the relationship between internal load measures. Researchers are encouraged to apply the Linear Mixed Models rather than correlation to analyze internal load relationships in team sports since it allows for the consideration of the individuality of players