Biology subjects

Isaka, T.

Publications and source records attributed to Isaka, T..

3 recordsLinked to original sources

bioRxiv2026

Muscle-specific reticulospinal contributions to limb-trunk coordination during standing arm curls in strength-trained and untrained individuals

Limb-trunk coordination plays an essential role in daily actions. The reticulospinal excitability of limb muscles has been suggested to be modulated by long-term motor experience, such as strength training. However, it remains unclear whether reticulospinal contributions in the limb and trunk muscles during limb-trunk coordinated movements are modulated by strength training. This study aimed to determine whether reticulospinal contributions to limb-trunk coordination differ between strength-trained and untrained individuals. Fifteen long-term ([≥]3 yrs) strength-trained and 15 untrained healthy men participated in this study. Participants performed a rapid bilateral arm-curl task while standing, using a load corresponding to 35% of their one-repetition maximum, in response to visual, visual-auditory (80 dB), or visual-startling (115 dB) stimuli. Electromyography (EMG) was recorded from the right biceps brachii (BB) and erector spinae (ES) muscles during the task. In the trained group, EMG onset of the ES was closer to that of the BB than in the untrained group, indicating tighter temporal coordination between the limb prime mover and trunk postural muscles in strength-trained individuals. In both groups, visual-startling stimuli shortened the EMG onset of both the BB and ES, suggesting reticulospinal contributions to both muscles. Notably, the reduction in EMG onset of the BB induced by the startling stimulus was smaller in the trained group than in the untrained group, whereas no difference between groups was observed for the ES. These findings suggest that long-term strength training may modify limb-trunk muscle coordination during standing arm curls and may be associated with muscle-specific adaptations in reticulospinal contributions.

neuroscience↗

bioRxiv2025

Individual bounded rationality destabilizes cooperative dynamics in human-AI groups

Cooperative dynamics arise from interactions among individuals, including humans and artificial agents, yet it remains unclear how individual-level cognition and motion shape collective dynamics in such human-AI groups. We combined a dynamic cooperative task, in which one attacker was controlled by a human and two by heuristic artificial agents facing a deep reinforcement learning defender, with counterfactual simulations of artificial groups. Across nine task conditions, groups including a human consistently underperformed relative to groups composed solely of artificial agents. Humans exhibited restricted movement options and probabilistic rather than deterministic action choices, which shifted coordination dynamics towards less symmetric, less organized patterns and reduced performance for both individuals and groups. Embedding these boundedly rational movement and decision parameters into artificial agents reproduced human-like behavior and performance declines. These results demonstrate how limitations of a single individual can destabilize cooperative dynamics and provide insights into the design of robust human-AI systems.

animal behavior and cognition↗

bioRxiv2018

Cross-sectional and longitudinal research approaches: running pace and step characteristics of elite athletes in the 400-m hurdles

The aim of this study was to clarify the running pace and step characteristics among various competitive-level 400-m hurdlers through cross-sectional and longitudinal research approaches. We analysed spatiotemporal data for 13 male world-class and 14 male national-level 400-m hurdlers. We analysed 16.8 {+/-} 4.2 races for each world-class hurdler and 20.0 {+/-} 6.0 races for each national-level hurdler (the total number of analysed runs was 499) using publicly available television and internet broadcasts. Cross-sectional approach showed that positive relationships of finish time were highly obtained between both first- (r = 0.901) and latter-half split times (r = 0.914). In contrast, the first- and latter-half split times were not significantly correlated to SL and SF. A multiple single-subject approach showed that 14/27 hurdlers were identified as being latter-half speed reliant. In contrast, no hurdlers demonstrated first-half reliance. In the latter half of the race, 12/27 hurdlers were identified as being SF reliant; no hurdlers demonstrated SL reliance. In conclusions, important findings regarding high performance in a cross-sectional research approach do not always corresponded with those in a longitudinal research approach. Athletes and coaches should carefully improve performance in the first half of the race based on an individualization principle for training.

physiology↗