CrossFit has been shown to improve cardiovascular health, body composition and muscle strength. Findings of a new study, however, suggest of unwanted effects associated with doing CrossFit-style workouts for at least two consecutive days.

Those new to CrossFit based training (CFBT), in particular, should consider adopting a rest day to take a break from two straight days of doing hard workouts. Otherwise, they risk impairing their immune system as consecutive CrossFit workouts can reduce the level of anti-inflammatory immune system proteins.

Those who advocate for varied and high intensity workouts claim that these significantly improve physique and overall fitness in a shorter span of time. The results are also balanced across all of the body's muscles.

An earlier research, however, has shown that repeated bouts of high-intensity exercise can stress the body and temporarily impair immunity prompting Ramires Tibana, from the Catholic University of Brasilia in Brazil, a CrossFitter himself, to conduct an investigation.

Tibana and colleagues recruited nine male CrossFitters who had been involved with the fitness program for at least six months. The participants did intense CrossFit-style workout for two consecutive days, which include Olympic lifting, strength-training moves, powerlifting and gymnastic drills.

After each workout, Tibana and his team measured the muscle power of the participants. They also looked at the levels of metabolic markers in the blood and inflammatory cytokines, the proteins produced by the white blood cells, which help protect the body from infection and illness.

After the second day, the researchers found that while intense exercise did not compromise the muscular strength of the CrossFitters, it reduced the levels of the cytokines.

"In conclusion, two consecutive days of CrossFit training elicited a significant decrease in anti-inflammatory cytokines without impairments in muscle power," Tibana and colleagues wrote in their study, which was published in Frontiers in Physiology on June 28.

"While we observed no negative effect on muscular power, it is still recommended that caution be exercised due to the suppressive effect two consecutive days of CFBT had on the immune system."

Although the findings did not show that workout can increase vulnerability to illness and that CrossFit is not safe, Tibana and colleagues suggested that CrossFitters, particularly beginners, should take more rest than people with higher fitness levels. The recommendation also applies to those recovering from illness, who may already suffer from impaired immune response.

"A rest day is important for recovery for subsequent training sessions," Tibana said. "Other alternative recovery techniques are regenerative training (with low intensity and volume), massage and cryotherapy."

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