Cardiorespiratory Fitness Improvements Following Low‐Frequency Training Are Not Inferior to High‐Frequency Training Matched for Intensity and Volume

Epidemiological evidence suggests low-frequency physical activity provides health benefits, but the physiological impacts of weekly training frequency are understudied. We investigated whether "Weekend Warrior" (WW) training was inferior to traditional, high-frequency (HF) training for improving maximal oxygen uptake (V̇O₂max). The secondary aim was to assess integrative physiological adaptations to each protocol. Twenty-eight sedentary-to-recreationally-active adults aged 18-45 years (14 males and 14 females) were randomized to perform 8-weeks of HF or WW training on a cycle ergometer (either four or two sessions weekly, respectively), consisting of continuous and interval exercise, with intensity and volume matched between groups. WW training was not inferior to HF training for improving V̇O₂max (mean ± standard deviation; WW: 43.5 ± 6.5 vs. 47.8 ± 6.4 mL/kg/min; HF: 42.3 ± 6.2 vs. 47.3 ± 6.7; main effect of training, p < 0.001). Severe domain cycling time-to-task-failure also increased in both groups (WW: 3.7 ± 1.6 vs. 8.6 ± 3.2 min; HF: 3.5 ± 0.9 vs. 7.7 ± 2.8; main effect of training: p < 0.001). Frequency did not affect improvements in hemoglobin mass (WW: 771 ± 203 vs. 790 ± 189 g; HF: 754 ± 185 vs. 765 ± 202; main effect of training: p = 0.043) or skeletal muscle oxidative capacity (WW: 0.034 ± 0.008 vs. 0.045 ± 0.015 s^-1; HF: 0.036 ± 0.011 vs. 0.041 ± 0.010; main effect of training: p = 0.002), nor did it influence improvements in cardiorespiratory, substrate oxidation, voluntary muscle contractile, and perceptual responses to submaximal exercise (interaction effect: p > 0.05 for all outcomes). Eight weeks of training improved V̇O₂max and a wide range of physiological outcomes with no difference between training frequencies, suggesting that the distribution of weekly exercise volume has a limited effect during short-term training. Trial Registration: This trial was registered at ClinicalTrials.gov identifier: NCT05908578.