The energy cost of cycling in young obese women

Abstract

In order to evaluate the difference in the energy cost of submaximal cycling between normal weight (NW) and obese (OB) females, nine OB (age 23.2 years+/-1.6 SE, BMI 40.4+/-1.2 kg/m2) and nine NW (age 25.6 years+/-1.8, BMI 21.7+/-0.6 kg/m2) healthy young women were studied during a graded bicycle ergometer test at 40, 60, 80, 100 and 120 W. At rest and at all workloads, oxygen uptake VO2 was higher in OB than in NW women (Student's t test, P<0.05-0.01), as well as respiratory quotient during all exercise levels (P<0.05-0.01), while similar values of heart rate, pulmonary ventilation and breathing efficiency were found between the two groups. Maximal VO2 and anaerobic threshold were higher in OB women, and they also explained the higher oxygen pulse observed during submaximal exercise, but no difference was found when the values were adjusted for fat-free mass. While net mechanical efficiency (ME) was significantly lower in OB (ANOVA, P<0.05), delta ME was similar in both groups, indicating no substantial derangement of muscle intrinsic efficiency in obesity, but suggesting that the increased mass of body segments involved in cycling movements may be chiefly responsible for the higher energy cost of this type of exercise. Comparison of the actual VO2 presently measured with that predicted by available cycle ergometry equations at the different workloads indicated inaccuracy of various degrees ranging from 8.4 to -31.9%. It is concluded that the lower mechanical efficiency displayed by obese women in cycling has to be taken into account when prescribing exercise through methods predicting the metabolic load.

The energetic and cardiovascular response to treadmill walking and cycle ergometer exercise in obese women

“…The energy required to sustain a given bicycle workload has been previously shown to be correlated with body mass to a various degree by different studies, when explored in a continuum from normal weight to overweight (Berry et al 1993;Cotes 1969). In the present investigation, when cycling at submaximal levels, OB women consumed more energy (in mean about 23%) than NW women, at all the investigated metabolic intensities, in agreement with previous findings obtained in obese subjects of both genders with different age and degree of obesity (Hulens et al 2001;Salvadori et al 1999, Lafortuna et al 2006. While the greater VO 2 observed at rest and estimated in maximal conditions in OB may be considered as the consequence of a larger FFM and muscle mass (Bosy-Westphal et al 2004;Goran et al 2000), the greater values displayed at submaximal work are related to a higher energy cost of the specific motor activity.…”

“…4b, c). This is consistent with the results concerning delta efficiency previously reported in extremely obese women (Lafortuna et al 2006). Similar trends in net and work efficiency during cycling in relation to body mass were reported by Berry et al (1993) in a group of normal weight women.…”

“…In turn, the energetics of TM locomotion in moderately obese subjects of both genders was studied by Browning et al (2006), who reported that the cost of walking, per unit body mass and unit distance, is higher in the obese, but the effect of extreme obesity was not investigated. We recently studied the cost of cycling in a homogeneous group of young healthy extremely obese women (Lafortuna et al 2006) and we reported energy expenditure about 20% higher in the obese group, but we could not assess the energetics of TM walking in those same women.…”

Skeletal muscle oxidative function in vivo and ex vivo in athletes with marked hypertrophy from resistance training

“…Moreover, despite the significantly greater body mass, during CE, no impairment of oxidative function was seen in RTA at submaximal work rates: the efficiency and the "O 2 cost" of exercise (as indicated by the slopes and the intercepts of the V O 2 vs. work rate relationships) were indeed the same in the two groups. This finding is of interest, also compared with what is usually seen in another population characterized by a significantly greater body mass, such as obese patients, in which the V O 2 vs. work rate relationship is shifted upward compared with that seen in normal controls (22), indicating a higher O 2 cost of CE exercise deriving from the excess in body mass.…”

Acquired obesity and poor physical fitness impair expression of genes of mitochondrial oxidative phosphorylation in monozygotic twins discordant for obesity

“…Previous studies expressing V O 2max per kilogram LBM have shown either decreased (9,22,23,67,69) or unchanged (12,18,34,40) V O 2max in obese compared with nonobese subjects. Possibly, genetic differences as well as those in age, sex, family environment, and physical activity could, together with small sample sizes, have confounded comparison of obese and nonobese subjects in the latter studies (12,18,34,40).…”