Impact of Intensity-Specific Aquatic Cycling Training on Muscle Strength, Cardiorespiratory Fitness, Neurotrophic Factors, and Cognitive Function Among Older Women

Background This study investigated the effects of aquatic cycling training (ACT) at varying intensities on muscle strength, cardiorespiratory fitness, brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), and cognitive function among older women. Methods Forty women aged 65–74 years were randomly assigned to one of four groups: high-intensity interval ACT (HIIT; n = 10), moderate-intensity continuous ACT (MICT; n = 10), progressive-intensity ACT (PICT; n = 10), and control groups (n = 10). The intervention was conducted over 16 weeks, with three sessions weekly. Muscle strength (represented by isokinetic knee strength), cardiorespiratory fitness, BDNF, IGF-1, and cognitive function were measured before and after the intervention. A two-way repeated-measures (RM) analysis of variance (ANOVA) was performed to examine differences across groups and time. Results Knee extensor strength significantly improved across all training groups (p < 0.01), with between-group differences observed. Knee flexor strength significantly increased in the HIIT and PICT groups (p < 0.01), with partial differences between groups. Both BDNF and IGF-1 levels significantly increased across all training groups (p < 0.01), with confirmed group differences. Cognitive function improved significantly across all training groups, but no intensity-based differences were found. Conclusions Sixteen weeks of ACT produces beneficial effects on functional fitness (represented by muscle strength and cardiorespiratory fitness), BDNF, IGF-1, and cognitive function among older women, irrespective of training intensity. Improvements in muscular strength and neurotrophic factors were influenced by exercise intensity, whereas cognitive gains were independent of intensity. These findings indicate that ACT is an effective and safe intervention for enhancing physical fitness and promote neuroplasticity, thereby contributing to improved cognitive function among older women. Trial registration Clinical Research Information Service (CRIS), KCT0011903. Registered 27 April 2026 (Retrospectively registered).