Fig. 4

Maximum oxygen uptake (VO_2max) in absolute terms in the morning, and in the afternoon, following the ingestion of caffeine or the placebo. Panel a: Individual observations for each subject (grey lines), and the mean for all subjects (black line). Panel b: Individual observations for each subject (black dots), standard deviation and minimum/maximum values (box-and-whisker plot), and P value obtained by two-way ANOVA. Similar letters (i.e. a-a; b-b, etc) indicate significant post hoc differences. VO_2max relative to weight in the morning, and in the afternoon, following the ingestion of caffeine or the placebo. Panel c: Individual observations for each subject (grey lines), and the mean for all subjects (black line). Panel d: Individual observations for each subject (black dots), standard deviation and minimum/maximum values (box-and-whisker plot), and the P value obtained by two-way ANOVA. Similar letters (i.e. a-a; b-b, etc.) indicate significant post hoc differences