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Oxygen uptake kinetics slower during, after exercise in women with subclinical hypothyroidism
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Compared to those with no thyroid condition, women with subclinical hypothyroidism have slower pulmonary oxygen uptake kinetics during transitions from rest to exercise and exercise to recovery, according to recent findings.
For the study, researchers recruited 38 women between the ages of 20 and 55 years from the Department of Endocrinology, Maternity Hospital Therezinha de Jesus, School of Medical Sciences and Health of Juiz de Fora, Brazil. The study population consisted of 19 women with subclinical hypothyroidism (SCH) and 19 control volunteers with no thyroid impairment. The study participants were matched for age, BMI, physical activity and menopause status.
The sample size was established for purposes of comparing oxygen uptake (VO2) kinetics in two samples.
The volunteers engaged in an exercise test on an electronic ergometer bicycle. Volunteers sat resting on the bicycle for 3 minutes, followed by 6 minutes of exercise with a constant work load of 50 W while maintaining a rate of 60 rpm, followed by 6 minutes of recovery.
The investigators quantified VO2 kinetics by the mean response time (MRT), which estimates the time necessary to achieve 63% change in VO2 (∆VO2). They calculated the O2 deficit and O2 debit, which quantify both anaerobic metabolism during the transition to exercise and extra energy demand while transitioning to recovery, using the formula MRT x ∆VO2.
The researchers found that in the transition from rest to exercise, volunteers with SCH showed slower VO2 kinetics (MRT=47 seconds vs. 40 seconds, P=.004) and a higher oxygen deficit (580 mL vs. 477 mL, P=.003) than the control participants. In the transition from exercise to recovery, those with SCH also demonstrated slower VO2 kinetics (MRT = 54 seconds vs. 44 seconds, P=.001) and a higher oxygen debit (679 mL vs. 572 mL, P =.003) than controls.
According to the researchers, longitudinal studies on the effects of physical training on VO2 kinetics in SCH patients are needed to substantiate these findings.
“This finding indicates a possible impairment in the dynamics of supply and use of O2 in SCH patients during and after exercise,” the researchers wrote. “The degree of impairment may be associated with higher thyroid stimulating hormone levels.”
Disclosure: The researchers report no relevant financial disclosures.
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