In a randomised clinical trial of 464 sedentary post-menopausal women, it was shown that walking to achieve a calorie expenditure of just 4 calories per kg of body weight per week improved overall cardiorespiratory fitness, with a linear dose response seen with increased duration of walking. Exercise at 4 cal/kg per week is roughly equivalent to walking 15 mins per day for 5 days each week and is around 50% of the amount of physical activity previously recommended by health authorities.
In this study, women were randomised to a placebo comparison group, as well as to exercise intervention groups where participants would walk or cycle to obtain an energy expenditure of 4, 8 or 12 cal/kg per week (each category is equivalent to an average of 72, 136 and 192 minutes of moderate exercise per week). The primary outcome measure was peak absolute oxygen consumption (VO2 max) which has been widely recognised as an accurate measure of cardiorespiratory fitness and endurance capacity.
Each group included in the study showed clear linear dose-response improvements in physical fitness (VO2 max) of 4.2% in the 4cal/kg, 6% in the 8cal/kg and 8.2% in the 12 cal/kg per week groups after six months; but there was no change in average weight, cholesterol levels or blood pressure in each group.
The study demonstrates that even small amounts of physical activity such as walking and cycling may be beneficial for general health and fitness and that intense physical activity may not be required in order to obtain some improvement in fitness level. This is great news for those with disabilities or injuries that may prohibit more intense forms of physical activity and may provide an entry level physical activity regime for sedentary people to make fitness gains.
In another study titled the 'Women's Health Study' it was demonstrated that women who walked as little as 1 or 1.5 hours per week had half the risk of developing coronary heart disease than sedentary women. In this cohort study of 39,000 individuals, it was found that time spent walking, but not walking pace, resulted in lower coronary heart disease risk. The risk reduction from at least 1 hour per week spent walking, was present even in those women determined to be at high risk of coronary heart disease, including women who smoked, were overweight or had high cholesterol.
All data considered, it is clear that all exercise, regardless of intensity may be beneficial for health and fitness, with a promising dose-response relationship with greater time spent exercising.
References:
1. Lee I. Dose-Response Relation Between Physical Activity and Fitness. JAMA [Internet]. 2007;297(19):2137. Available from: https://jamanetwork.com/journals/jama/article-abstract/207060
2. Lee I, Rexrode K, Cook N, Manson J, Buring J. Physical Activity and Coronary Heart Disease in Women. JAMA [Internet]. 2001;285(11):1447. Available from: https://jamanetwork.com/journals/