The Effect of Sprint Interval Training on Body Composition of Postmenopausal Women

Yati N. Boutcher; Stephen H. Boutcher; Hye Y. Yoo; Jarrod D. Meerkin

Disclosures

Med Sci Sports Exerc. 2019;51(7):1413-1419. 

In This Article

Discussion

The major findings of this study were that 8 wk of SIT resulted in increased trunk and leg lean mass, decreased total fat mass, and increased aerobic fitness of postmenopausal women after only 8 h of actual exercise over 8 wk.

Lean body mass. Eight weeks of SIT resulted in a 0.7-kg increase of lean body mass. Other SIT studies have produced a similar or greater lean mass gain. It was found that there was an increase in trunk muscle mass of 0.6 kg after 15 wk of SIT in young women[7] and a significant 1.2 kg increase in lean body mass of overweight males after 12 wk of SIT.[9] In type 2 diabetic postmenopausal women 16 wk of SIT produced a 0.5-kg increase in total lean mass.[11] The present study extends these results by demonstrating that 8 wk of SIT can also result in an increase in the lean mass of nondiabetic but overweight postmenopausal women. Lean mass preservation or gain is especially important for postmenopausal women as it acts as a reservoir of essential amino acids that are needed to maintain the function of numerous organs.[22] Lean mass also protects against type 2 diabetes mellitus development. Insulin resistance is a precursor to the development of type 2 diabetes and occurs when muscle loses its responsiveness to insulin signaling.[23]

The ability of SIT to reduce insulin resistance has been well established,[24] thus future research should examine the effects of SIT on the insulin resistance of postmenopausal women. Interestingly, the 0.7-kg increase in lean mass in the present study was predominately in the trunk and legs which is consistent with previous studies.[7–10] The 0.7-kg total increase in lean mass after 8 h of SIT equates to an 86-g gain per hour of SIT. This increase compares favorably to that achieved after exposure to regular resistance exercise. It was found that a three times per week, hourly resistance program given to sedentary postmenopausal women for 10 wk resulted in increased total lean mass of 1.2 kg, which equated to a 40-g gain in lean mass per hour.[25] Similarly, a 16-wk weight training program increased total lean mass of overweight postmenopausal women by 2 kg which also equated to a 40-g gain in lean mass per hour.[26] Thus, weight training resulted in significant increases of lean mass of the arms, chest, trunk, and legs of postmenopausal women whereas SIT increased lean mass of the trunk and legs only. Future research is required to confirm the lean mass increase brought about by SIT.

This increase in lean mass supports results of prior research that has investigated the effects of high-intensity exercise on muscle characteristics and remodeling. After nine cycling high-intensity intermittent training (HIIT) sessions by young males a significant increase in muscle protein synthesis was found.[27] A shorter 3-wk HIIT program examining obese men and women also demonstrated a significant HIIT-induced increase in muscle size.[14] The exposure of type 2 diabetic men to 8 wk of continuous high-intensity exercise (two sessions per week for 45 min at 75% V̇O2peak) resulted in a 24% increase in mid-thigh cross-sectional area.[28] A large increase in mitochondrial and myofibrillar protein synthesis, 24 to 28 h after one bout of continuous high-intensity exercise, has also been found.[29] These studies have typically examined muscle remodeling in the legs which were actively involved in high-intensity cycle exercise. The reason behind the increase in trunk lean mass found in the present and past studies,[7–10] using the 8 s/12 s sprint protocol, is unclear. In this protocol participants perform approximately 1000 sprints during the 20 min of exercise equating to approximately 3.7 miles (5.6 km) of sprint distance when extrapolated to actual cycling. The 8 min of total time of sprinting in the 8 s/12 s sprint protocol is likely to involve constant isometric contraction of the trunk muscles which may have driven the increase in lean mass. For example, 16 wk of HIIT using upper and lower body ergometers resulted in significant increases in cross-sectional area of the musculus anterolateral abdominal area,[30] however, no increase was found in a group that only used lower body ergometer. Training involved eight to 12 sets of high-intensity cycling exercise for 60 s with a 60-s active rest period. Thus, future research is needed to examine the regional muscle mass effects of high-intensity interval protocols that vary in their intensity and sprint rate.

Fat mass. The SIT group reduced their total fat mass by 0.4 kg after 8 wk. This result confirms results of previous SIT studies that have also demonstrated a significant decrease in the total fat of overweight adults.[7–10] The decrease in fat mass that occurred mostly in the trunk and legs, however, was smaller when compared to previous studies.[7–10] In a 15-wk SIT program examining normal weight premenopausal women a reduction of 2.5 kg of subcutaneous was found,[7] whereas a 12-wk SIT intervention with overweight premenopausal women resulted in a 2.6-kg decrease.[8] The smaller fat loss occurring in the present study maybe a result of the shorter length of the SIT program (8 wk) and hormonal imbalance brought about by menopause that may have impeded SIT-induced fat loss.[1] Genetic and behavioral factors such as compensatory eating or reductions in daily physical activity may also have influenced subcutaneous fat change.[31] The possible mechanism underlying the SIT-induced fat loss effect most likely involves increased fat oxidation during and after exercise. Toward the end of a HIIT session that consisted of ten 6-s bouts of maximal sprints, an inhibition of anaerobic glycogenolysis occurred and ATP resynthesis was mainly derived from intramuscular triacylglycerol stores.[16] That SIT progressively results in greater fat oxidation is also supported by Trapp et al.[32] who found increased venous glycerol levels during SIT in both trained female cyclists and untrained women. Also, it has been shown that six to seven sessions of HIT had marked increases in whole body and skeletal muscle capacity for fatty acid oxidation.[33]

Visceral adipose tissue. There was no significant reduction in visceral fat after SIT in these postmenopausal women. Previous studies have shown that SIT effectively reduces visceral fat of overweight young adults. A 9.5% reduction was found after a 15-wk protocol[7] and 12 wk of SIT brought about a 17% reduction in the visceral fat of young men.[9] Also, a significant reduction of visceral fat by 5.7% was found after 16 wk of SIT administered to overweight postmenopausal women.[11] Why these postmenopausal women did not lose visceral fat after SIT is unclear but may involve the decrease in estrogen that accompanies menopause which causes an increase in blood levels of insulin resulting in the promotion of fat deposition and a blunting of fat oxidation.[1,12] Decreased fat oxidation response to SIT in conjunction with the central redistribution of fat that accompanies menopause may have contributed to the failure of SIT to result in a decrease of visceral fat in these postmenopausal women.[34] As mentioned in the previous paragraph amount of SIT exposure and behavioral compensation may also have influenced the lack of visceral fat change found in these postmenopausal women.[31]

Aerobic fitness. After 8 h of SIT, the exercise group significantly improved their absolute predicted V̇O2max by 12% which is consistent with results of a meta-analysis that indicated that SIT and other forms of interval training-induced improvements in aerobic fitness that were superior to that of traditional aerobic exercise training.[15] The aerobic fitness changes found in the present study were less compared with a study that used 15 wk of SIT using the same protocol[7] where young women improved their V̇O2max by 24%. Also, a significant 15% increase was demonstrated after a 12-wk lifestyle intervention that included SIT as the exercise component.[8] That the present study found a smaller improvement in V̇O2max compared with these other SIT interventions may be because of the shorter duration of the SIT intervention, the cardiovascular deterioration that occurs with aging and menopause, and/or the loss of estrogen occurring before and during menopause.[34] Improvements in anaerobic fitness were suggested by increases in rpm, load, and power when HR stayed constant. Thus, after 8 wk of SIT participants were able to generate significantly more power at similar exercise HR.

That SIT so effectively improves aerobic fitness in a short period reflects the unique nature of SIT which comprises of significant amounts of both aerobic and anaerobic exercise.[35] SIT-induced increases in aerobic fitness may be brought about by central and peripheral adaptations that include changes in autonomic function, cardiac output, mitochondrial activity, vascular, and skeletal muscle metabolic capacity.[36] SIT increases in V̇O2max are superior[15,37] or equal[36,38] to traditional aerobic endurance training despite much shorter exercising time. As the most prominent barrier to exercise has been cited as "perceived time"[39] the ability of SIT to increase aerobic fitness in minimal time may have significant clinical value as low aerobic fitness has been established as a major predictor of mortality.[40]

One of the limitations of this study is that the majority of women were Caucasian and thus results may not be generalizable to other ethnic groups. Also, women were primarily recruited from University staff and thus were more likely to be better educated than the general population. Also, it would have been beneficial to include an aerobic exercise training group in the study design. Although SIT compared to aerobic training has demonstrated superior changes in fat and lean mass and aerobic fitness of premenopausal women[32] this effect has not been verified in postmenopausal women.

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