Sex differences in the effects of 12 weeks sprint interval training on body fat mass and the rates of fatty acid oxidation and VO₂max during exercise

Abstract

BackgroundThe purpose of this study was to examine whether very short duration, very high intensity sprint interval training (SIT) leads to loss of body fat mass in association with improvements to VO2max and fatty acid oxidation, and to assess the extent of sex dimorphism in these physiological responses.MethodsA total of 24 men and 17 women (mean (SEM) age: 39 (±2) years; body mass index 24.6 (0.6)) completed measurements of the maximal rate of oxygen uptake (VO2max) and fatty acid oxidation (FATmax). Body fat and lean mass were measured by dual emission x-ray absorptiometry, and fasting blood lipid, glucose and insulin profiles were assessed before and after training. SIT consisted of 4×20 s sprints on a cycle ergometer at approximately 175% VO2max, three times per week for 12 weeks.ResultsFat mass decreased by 1.0 kg, although men lost statistically significantly more fat than women both when expressed in Kg and as % body fat. VO2max increased by around 9%, but women improved VO2max significantly more than men. FATmax improved by around 13%, but fasting plasma glucose, insulin, total triglyceride, total cholesterol and high-density lipoprotein (HDL) did not change after training, while low-density lipoprotein decreased by 8% (p=0.028) and the HDL:Total Cholesterol ratio improved by 6%. There were no sex differences in these metabolic responses to training.ConclusionsThese results show lower body fat %, and higher rates of fatty acid oxidation and VO2max after 12 weeks of training for just 4 min per week. Notably, women improved VO2max more than men, while men lost more fat than women.

High‐intensity interval training improves insulin sensitivity in older individuals

“…We found no change in plasma FFA or triglycerides, while HDL decreased slightly, but only in females. Other studies have found a reduction in LDL concentration or no change in either of these lipid parameters after 12 weeks of HIIT in young or older subjects . The contrasting findings with the present study may be explained by the fact that subjects in the present study had a less healthy lipid profile at baseline compared to the two other studies.…”

“…It is further unclear if the response to HIIT is gender specific as HIIT studies including both males and females often report pooled effects . However, some studies have found differential gender responses to HIIT showing a higher reduction in body fat and indicated improved insulin sensitivity (Cederholm index) in males and increased VO 2 max in females …”

Inter-individual responses to sprint interval training, a pilot study investigating interactions with the sirtuin system

“…This is supported by a recent study reporting sex differences in response to 12 weeks of sprint interval training (Bagley et al 2016). …”

Mechanistic and methodological perspectives on the impact of intense interval training on post‐exercise metabolism

“…When protocols are not matched, MICT tends to produce greater reductions in total body fat percentage compared to HIIT and SIT as a whole, though Wingate‐based SIT (performed in an “all‐out” manner) on its own produces body fat reductions comparable to MICT in less time . Nevertheless, the ability of HIIT/SIT to reduce fat mass irrespective of MICT is well‐supported, and these improvements in body composition have been demonstrated in several populations, including recreationally active women and men, untrained women, inactive overweight women, and overweight or obese men …”

“…64 Nevertheless, the ability of HIIT/SIT to reduce fat mass irrespective of MICT is well-supported, and these improvements in body composition have been demonstrated in several populations, including recreationally active women 11,65 and men, 65 untrained women, 66 inactive overweight women, [67][68][69][70] and overweight or obese men. [70][71][72][73][74] The mechanisms underlying the observed fat loss are not well understood, though it has been proposed that the EPOC induced by HIIT/SIT is a potential contributor. 10,30,38,44 Due to the intense nature of the protocol, it is often hypothesized that HIIT/SIT elevates EPOC to a greater extent than MICT, and over the course of the day may result in an energy deficit not accounted for in the estimated caloric expenditure associated with the session itself.…”