The effects of heavy load carriage on physiological responses to graded exercise.

PURPOSE: Many emergency response occupations require heavy load carriage with backpacks. The purpose of this experiment was to study the effects of heavy load carriage on physiological responses and performance during graded exercise. METHODS: Fifty males (age: 28 ± 6 years, height: 182.8 ± 6.2 cm, mass: 85.4 ± 12.1 kg) provided written informed consent before completing two randomly ordered graded exercise tests to measure ventilatory threshold and peak oxygen consumption (˙VO2peak). During the loaded test, each subject carried a correctly sized and fitted 80 L backpack weighing 25 kg. Mass, volume and load distribution were consistent between all packs. Modified Balke treadmill tests were completed by walking at 1.5 m s(−1) with stage increases of 2% grade until exhaustion. RESULTS: Analysis revealed a small but significant decrease in ˙VO2 at ventilatory threshold (3.9%) and peak exercise (2.5%) under load. Power output at ventilatory threshold and ˙VO2peak were significantly decreased by 23.6 and 11.1%, respectively, and test duration was reduced by 29.8% in the loaded condition. CONCLUSIONS: While heavy load carriage had relatively small effects on physiological responses at ventilator threshold and peak exercise, the reductions in power output and test duration were more substantial. Despite the absolute mass of the pack and the large range of subject size, the only change in performance associated with body size was test duration. These results have implications for evaluation of fitness for duty in occupations where heavy load carriage is required.

The association between physical activity and liver fat after five years of follow-up in a primary prevention multi-ethnic cohort.

OBJECTIVE: Excess liver fat (LF) is associated with dyslipidemia, insulin resistance and cardiovascular disease. Evidence suggests that there is an independent relationship between physical activity (PA) and LF although little is known of the role of PA intensity in reducing LF. The purpose was to evaluate whether meeting PA guidelines, the amount of PA and the intensity of PA at baseline were associated with LF after five-years. METHODS: Men and women (n=478) living in Vancouver, Canada of Aboriginal, Chinese, European or South Asian background completed baseline measurements in 2004-2005. Liver fat was assessed using CT scans at 5-year follow-up, and PA using a PA questionnaire at baseline as well as demographics and anthropometry. RESULTS: In separate unadjusted models, meeting moderate-vigorous PA (MVPA) guidelines (p=0.009), vigorous PA (p=0.002) and MVPA (p=0.017) but not moderate PA (p=0.068) was predictive of LF at five years (p=0.009). In multiple linear regression models, when adjusted for covariates, meeting MVPA guidelines and MVPA with LF at five years was no longer significant (p>0.05) while vigorous PA remained significant (p=0.021). CONCLUSION: Meeting PA guidelines through MVPA may not be adequate to prevent the accumulation of LF and PA guidelines may require revision. Vigorous PA should be encouraged to prevent LF accumulation.

The association between cardiorespiratory fitness and abdominal adiposity in postmenopausal, physically inactive South Asian women.

In South Asians, a unique obesity phenotype of high abdominal fat is associated with increased cardiovascular risk. Low cardiorespiratory fitness (CRF) is associated with abdominal fat and an increased risk of cardiovascular disease. The purpose of this paper is to determine whether CRF as assessed by VO2 peak, in post-menopausal South Asian women, was associated with body fat distribution and abdominal fat. Physically inactive post-menopausal South Asian women (n = 55) from the Greater Vancouver area were recruited and assessed from January to August 2014. At baseline, VO2 peak was measured with the Bruce Protocol, abdominal fat with CT imaging, and body composition with dual energy X-ray absorptiometry. ANOVA was used to assess differences in subcutaneous abdominal adipose tissue (SAAT), visceral adipose tissue (VAT) and total abdominal adipose tissue (TAAT) between tertiles of CRF. Bivariate correlation and multiple linear regression analyses explored the association between VO2 peak with SAAT, VAT, TAAT and body composition. Models were further adjusted for body fat and body mass index (BMI). Compared to women in the lowest tertile of VO2 peak (13.8-21.8 mL/kg/min), women in the highest tertile (25.0-27.7 mL/kg/min) had significantly lower waist circumference, BMI, total body fat, body fat percentage, lean mass, SAAT, VAT and TAAT (p < 0.05). We found VO2 peak to be negatively associated with SAAT, VAT and TAAT, independent of age and body fatness but not independent of BMI. Further research is necessary to assess whether exercise and therefore improvements in CRF would alter SAAT, VAT and TAAT in post-menopausal South Asian women.