Cardiorespiratory Fitness At Baseline And In Response To Training Across Metabolic Health And Weight Phenotypes

BACKGROUND: Cardiorespiratory fitness has been proposed to be included as part of the metabolic health and weight status phenotype. The present study sought to examine how metabolic health/weight status is associated with changes in fitness in response to exercise training. METHODS: Participants (n = 718) from HERITAGE completed a 20-week training program and four groups based on baseline BMI and metabolic risk were created: metabolically healthy normal weight, MHNW; metabolically unhealthy normal weight, MUNW; metabolically healthy overweight/obese, MHO; and metabolically unhealthy overweight/obese, MUO. Unhealthy was defined as having ≥2 metabolic syndrome components: high blood pressure, fasting triglycerides, fasting glucose, and low HDL-C. VO2max was measured during two maximal exercise tests on a cycle ergometer at baseline and post-training. General linear models were used to examine differences at baseline and change in VO2max after adjusting for age, sex, and ethnicity (and baseline VO2max in change models only). RESULTS: There were no differences in baseline VO2max/kg between the normal weight groups (adjusted mean ± SEM: ~33.9 ± 0.5), which were higher than the values for the obese groups (p < 0.0001); MHO had higher VO2max/kg compared to MUO (28.8 ± 0.3 vs 27.5 ± 0.4, p = 0.004). The MUO group had a significantly (p ≤ 0.03) lower baseline VO2max/kg lean mass (41.2 ± 0.4) compared to values for all other groups, whose mean values were similar (~43.2 ± 0.5). All four groups experienced significant increases in VO2max with training. The MUO group showed the smallest increase in both VO2max/kg (4.2 ± 0.2) and VO2max/kg lean mass (5.9 ± 0.3), which was significantly different compared to values for all other groups for VO2max/kg (~5.6 ± 0.3). The MHO group showed the largest increase in VO2max/kg lean mass (7.4 ± 0.2), which was different (p ≤ 0.01) from values for the MHNW (6.6 ± 0.2) and MUO groups. CONCLUSIONS: Metabolically unhealthy obese adults had the lowest baseline values and experienced the smallest improvements in relative VO2max with training of any metabolic health/weight group. These findings support the notion that cardiorespiratory fitness may not only be a distinguishing characteristic of metabolic health, but also a potential target of treatment, particularly in obese adults.