Genetic limit of functional adaptability

Exercise tolerance in children and adolescents with musculoskeletal pain in joint hypermobility and joint hypomobility syndrome

OBJECTIVES

Musculoskeletal pain is a common complaint in a pediatric health care practice, but exercise tolerance has never been described in detail in these children. Our objectives for this study were to evaluate the maximal exercise capacity, including peak heart rate and oxygen consumption, of children with pain-related musculoskeletal problems, particularly in children with (symptomatic) generalized joint hypermobility and hypomobility, during a bicycle ergometry test to exhaustion; to evaluate muscle strength, bone mineral density, and sports activities in these children and to associate these observations with exercise capacity; and to compare these results with reference values.

METHODS

Thirty-two children (mean age: 12.1 years; SD: 3.4 years; range: 6.2-20.1 years; 62% male) with musculoskeletal pain-related syndromes (joint hypermobility syndrome [n = 13] and joint hypomobility syndrome [n = 19]) participated. The reference group consisted of 117 healthy primary school prepubertal children, 167 healthy secondary school adolescents, and 98 young adults (249 girls and 133 boys; mean age total reference group: 14.5 +/- 4.0 years; range: 8-20.8 years). Anthropometry, range of joint motion, muscle strength, bone mineral density (speed of sound and broadband ultrasound attenuation), sports activities, and a maximal exercise test using an electronically braked cycle ergometer were performed, and the patient stopped because of volitional exhaustion. Expired gas analysis and heart rate and transcutaneous oxygen saturation by pulse oximetry measurements also were performed.

RESULTS

Children with joint hypomobility syndrome as well as children with joint hypermobility syndrome had a higher mean z score (SD) of weight and BMI compared with the reference group. A significantly decreased absolute peak oxygen consumption and relative peak oxygen consumption in both patient groups was found compared with control subjects. In 14 of 32 children with a z score relative peak oxygen consumption of less than -2, maximal heart rate was significantly decreased compared with 18 children with a z score relative peak oxygen consumption of -2 or more (mean [SD] z score speed of sound: -1.3 [0.8] vs -0.5 [1.0] and mean [SD] heart rate: 175.9 [11.5] vs 187.5 [10.9], respectively). In the total group, a high significant correlation between the z score of relative peak oxygen consumption and the z score of the speed of sound was found as well as with z score of BMI. Sixteen (50%) of 32 participated in sports activities with (mean: 0.9 hours/week; SD: 1.4 hours/week), whereas in the control group, 12% of did not participate in sports activities (mean: 2.8 hours/week; SD: 2.2 hours/week). Children who participated in sports activities had a (borderline) significant increased mean (SD) z score of absolute peak oxygen consumption and mean (SD) z score of broadband ultrasound attenuation compared with children who did not participate in sports activities (-0.3 [1.1] vs -1.2 [1.3] and -0.45 [0.8] vs -0.9 [0.5], respectively).

CONCLUSIONS

In children with musculoskeletal pain-related syndromes, particular in children with (symptomatic) generalized joint hypermobility and hypomobility, maximal exercise capacity is significantly decreased compared with age- and gender-matched control subjects. The most probable explanation for the reduced exercise tolerance in our patients is deconditioning.

Effect of training intensity in adult females

The aim of this study was to investigate the effect of training intensity on maximal aerobic power on the basis of the subjects lean body mass. Seven sedentary adult females aged 23-40 years participated in a 44-week training experiment. They trained on a bicycle ergometer at progressive intensities of 60, 75, and 90% VO2 max for 13, 18, and 13 consecutive weeks, respectively. The total amount of work was between 9,000 and 12,000 kpm a day and frequency between 2 and 4 days a week, keeping both factors approximately constant for each subject throughout the 44-week training period. Mean VO2 max increased significantly during 60 and 90% VO2 max training. The increase during 75% VO2 max training was not significant. The final values during the three training periods were not necessarily the highest ones. Keeping the effect of age statistically constant, a significant partial correlation developed between the initial values and the total gains (%) of VO2 max, VE, and O2 pulse, expressed per lean body mass (LBM). The final attained values of VO2 max per LBM were significantly correlated with age. Therefore, if training intensity is sufficiently effective, it might be assumed that everyone has the same capacity for the improvement of cardiorespiratory function corresponding to their lean body mass, which is related to the magnitude of muscle mass. Furthermore, it might be said that the attainable level of aerobic power is greatly limited by the effects of age.

Maximal steady state versus state of conditioning

Criteria for the identification of maximal steady state as related to state of conditioning were evaluated. 13 volunteers walker and/or ran during a series of 15 min tests on a treadmill. The speeds ranged from mild to exhaustive. Heart rate was monitored continuously; VO2 was determined from 6 min to 9 min; and venous blood was obtained at 10 min and 15 min for lactate analyses. Max VO2 was established for each subject. Subjects were classified on level of conditioning according to the quantity and quality of their activity record for the previous 6 months. The 10 min heart rate associated with a blood lactate level of 2.2 mM/L (MSSHR) was the best predictor of conditioning. The relative VO2 (% of max VO2) found with a 10 min blood lactate concentration of 2.2 mM/L (RMSSVO2) was almost as accurate as MSSHR in predicting state of conditioning. Changes in blood lactate levels between 10 min and 15 min were not significantly related to conditioning.