The current study has shown that there are no differences in free-living MPS between young south Asian and white European men. Similarly were there any differences in the anabolic responses to resistance exercise training with similar increases in muscle and lean mass in South Asians and White Europeans. On the other hand, whilst total and lower body 1RM strength, and knee extensor torque increased to the same extent there was an attenuated increase in upper body 1RM strength in South Asians compared to white Europeans. Similarly, there were less favourable responses in total, visceral and subcutaneous fat, and in systolic blood pressure and VO2max in response to 12 weeks of resistance exercise training. No differences were seen, in response to resistance exercise training, between south Asian and white Europeans in the metabolic responses to a meal ingestion although there was a tendency for a less favourable response in insulin sensitivity, measured via the Matsuda index, in South Asians.
There have been very few studies which have previously looked at MPS or the anabolic effects of resistance exercise in south Asians. The current data would indicate in young healthy south Asian men MPS, measured during free-living habitual conditions, is not lower and is, thus unlikely, to underlie the lower muscle mass seen. However, whilst MPS is clearly important for muscle mass, it is not the only factor and does not necessarily associated with longer-term changes in muscle mass 22. Only one study, to our knowledge has investigated the effects of resistance exercise on muscle mass in South Asians with type 2 diabetes finding no effect of 12 weeks of progressive resistance training on lean body mass or muscle cross-sectional area,23. This is in contrast to the findings of the present study, where muscle mass appears to increase robustly in South Asians and may reflect differences in the measurement methods employed (DXA/CT vs MRI). It is also worth noting that there were no control groups without exercise training in these studies and so establishing the true effect of exercise is not possible. This is particularly important in a population, people with type 2 diabetes, where muscle mass will be declining 24.
The study of Misra made no measure of muscle strength, but this has been measured in the work of Knox et al 25,26. In response to a 6-week progressive resistance training programme, young healthy South Asian men were found to have similar increase in upper body strength, compared to White European men, although increases in lower body strength were attenuated in South Asians. In the current study, the opposite was seen with similar increases in lower body strength, but an attenuated increase in upper body strength. It is hard to make direct comparisons between these studies, as the study of Knox et al was only 6 weeks in duration, where increases in strength are at an early stage, and used a 3-repetition maximum protocol of only 2 exercises (squat and bench press) to measure strength. Taken together, however, the data does tentatively indicate there may be a slight attenuation in strength gains in south Asian men. It is worth emphasising that this was only one of our strength measures, and the finding may represent a type 1 error. It is also worth noting that robust increases in muscle strength (~ 23% for total 1RM) were still seen in South Asians, thus, resistance exercise should still be recommended to south Asians as the primary method to increase muscle mass and strength.
In both the Knox and Misra studies measure of body fat did not change with resistance exercise training in any groups. The current study found differential changes in total body, visceral and subcutaneous fat between South Asians and white Europeans in response to resistance exercise training, with changes less favourable in South Asians. This is a surprising finding, but may be partially supported by the observed difference in the effects of resistance exercise training on carbohydrate and fat oxidation that we observed. The reason for such a differential response to resistance exercise is not clear and warrants further study. Similarly, a differential response in systolic blood pressure was observed, with the decrease smaller in South Asians. It is known that South Asians have impaired endothelial function in forearm resistance vessels and a reduction in bioavailability of nitric oxide at rest and during exercise 27,28. It may, therefore, be that this observation reflects a reduced response of the vascular system to resistance exercise, but this clearly requires further investigation as the effects of exercise on blood pressure are multifactorial.
As our data demonstrated that increases in muscle mass and strength were similar in south Asians, compared to white Europeans, we may not have expected any differences in metabolic responses to the test meal administered. Indeed, there was no difference in fasting glucose, triacylglycerol and insulin or their responses to the test meal following resistance exercise training. There was, however, a trend for a difference in insulin sensitivity, as measured by the Matsuda index, with a small increase in White Europeans (1.80 95%CI: 0.21 to 3.95) which was not seen in South Asians (-1.13 95%CI: -3.40 to 1.14) which may be worthy of further study. It is worth noting again at this point that the study was not powered to detect differences in metabolic responses to exercise and these findings should be considered exploratory. In the study of Knox and colleagues 25, where insulin resistance was measured by HOMA-IR, no changes were observed in either White Europeans or South Asians, likely reflecting the short term nature of the study and the measure of insulin resistance employed. On, the other hand the study of Misra et al 23 found that insulin sensitivity increased and HbA1c decreased, with decreases similar in magnitude to those seen in with European populations in previous meta-analyses e.g. 6.
In conclusion, the current study has shown that free living MPS is not different between South Asians and White Europeans and that anabolic responses, gains in muscle strength and muscle mass, to resistance exercise broadly similar although these require confirmation in a larger study. We also provide some data which indicates that the cardiometabolic responses to resistance exercise training may be attenuated in South Asians, although again this requires further investigation in a larger study.
Perspective
Our results indicate that free living muscle protein synthesis is not different between young healthy South Asian and White European men making this an unlikely contributor to the lower muscle mass seen in South Asians. It may be possible that deficits in muscle protein synthesis may exist at different periods of the lifecourse and that there may be differences in muscle protein breakdown. These are worthy of investigation. South Asians are able to mount an anabolic response to resistance exercise training of a similar magnitude as White Europeans with similar increases in muscle mass and strength. However, the beneficial effects of resistance exercise on fitness, blood pressure, body fat and insulin sensitivity appear to be attenuated in South Asians although further work is needed to confirm this.