INS and obesity due to melanocortin 4 receptor deficiency: Lithgow et al. [35] demonstrated that HIIT (cycling for 1 min × 10 repetitions, 3 × week for 6 weeks) significantly reduced fasting insulin and glucose plasma levels, improving insulin sensitivity in males and females with overweight and obesity, whilst, interestingly, the addition of vitamin D3 appeared to attenuate the HIIT-induced improvement in glucose tolerance.