CrossFit® consists of workouts of the day (WODs) in which different exercises are conducted at high intensity with minimal or no rest periods. This study sought to quantify exercise intensity and muscular fatigue in the three CrossFit® session modalities: gymnastics (G), metabolic conditioning (M) and weightlifting (W). Thirty two, young, strength-trained, healthy men completed the three WODs: G (“Cindy”), M (double skip rope jumps) and W (power cleans). The variables measured in the sessions were: mean heart rate (HR), rate of perceived exertion (RPE), blood lactate [lactate], and jump height (H), average power (AP) and maximum take-off velocity (V_max) in a counter movement jump test. In all three WODs, elevated HR values (≥90% of the theoretical HR_max) were recorded at the time points mid-session and end-session. Mean RPEs were 17.6 ± 1.6 (G WOD), 16.0 ± 2.3 (M WOD), and 15.7 ± 2.0 (W WOD). Postexercise [lactate] was higher than 10 mmol·L^-1 for the three WODs. Following the G (“Cindy”) and W (power cleans) WODs, respectively, significant muscular power losses were observed in H (7.3% and 8.1%), V_max (13.8% and 3.3%), AP relative (4.6% and 8.3%) and AP total (4.2% and 8.2%) while losses in the M WOD were not significant (p > 0.05). A vigorous intensity of exercise was noted in all three WODs, with greater mean HRs detected in the “Cindy” and skip rope WODs than power clean WOD. Muscular fatigue was produced in response to the “Cindy” and power clean WODs but not the skip rope WOD.

• A vigorous intensity of exercise was noted in “Cindy”, Double Skip Rope jumps and Power Cleans WODs.

• Such high intensities of exercise have been related to cardioprotective benefits and described as a better way of improving VO_2max compared to more moderate work intensities

• However, trainers and exercise professionals need to be cautious when prescribing such high training intensities by making sure that individuals assigned to any Crossfit^® program are free of any cardiovascular or respiratory conditions or injuries that could jeopardize their health.

• The muscular fatigue observed here for the “Cindy” and Power Cleans WODs, but not for the Skip Rope Double Unders, suggests that for any high intensity exercise, recovery periods are essential to avoid muscle fatigue and injury.