I was considering dropping CrossFit in favor of a strength program when I came across an interesting study which compared Aerobic Training (AT) to Resistance Training (RT) for impact on Metabolic Syndrome (MS). (September 15, 2011, Volume 108, Issue 6, Pages 838–844. Comparison of Aerobic Versus Resistance Exercise Training Effects on Metabolic Syndrome (from the Studies of a Targeted Risk Reduction Intervention Through Defined Exercise – STRRIDE-AT/RT. Lori A. Bateman, Cris A. Slentz, PhD, Leslie H. Willis, MS, A. Tamlyn Shields, MS, Lucy W. Piner, MS, Connie W. Bales, PhD, RD, Joseph A. Houmard, PhD, William E. Kraus, MD.)
AT/RT induced a significant improvement in the MS z score (p = 0.004) and AT alone exhibited a trend toward improvement (p <0.07). However, RT alone failed to significantly alter the MS z score.
My conclusion is to stick with CrossFit and work in the resistance training as often as reasonable as an accessory to CrossFit.
Another view of the same data (J Appl Physiol (1985). 2015 Jun 15;118(12):1474-82. The effects of aerobic, resistance, and combination training on insulin sensitivity and secretion in overweight adults from STRRIDE AT/RT: a randomized trial. Abou Assi H, Slentz CA, Mikus CR, Tanner CJ, Bateman LA, Willis LH, Shields AT, Piner LW, Penry LE, Kraus EA, Huffman KM, Bales CW, Houmard JA, Kraus WE.). Conclusion:
AT/RT resulted in greater improvements in insulin sensitivity, β-cell function (disposition index), and glucose effectiveness than either AT or RT alone (all P < 0.05). Approximately 52% of the improvement in insulin sensitivity by AT/RT was retained 14 days after the last exercise training bout. Neither AT or RT led to acute or chronic improvement in sensitivity index. In summary, only AT/RT (which required twice as much time as either alone) led to significant acute and sustained benefits in insulin sensitivity.
Yet another look at the same data (Am J Physiol Endocrinol Metab. 2011 Nov;301(5):E1033-9. doi: 10.1152/ajpendo.00291.2011. Epub 2011 Aug 16.
Effects of aerobic vs. resistance training on visceral and liver fat stores, liver enzymes, and insulin resistance by HOMA in overweight adults from STRRIDE AT/RT. Slentz CA, Bateman LA, Willis LH, Shields AT, Tanner CJ, Piner LW, Hawk VH, Muehlbauer MJ, Samsa GP, Nelson RC, Huffman KM, Bales CW, Houmard JA, Kraus WE.) concluded:
AT was more effective than RT at improving visceral fat, liver-to-spleen ratio, and total abdominal fat (all P < 0.05) and trended toward a greater reduction in liver fat score (P < 0.10). The effects of AT/RT were statistically indistinguishable from the effects of AT. These data show that, for overweight and obese individuals who want to reduce measures of visceral fat and fatty liver infiltration and improve HOMA and alanine aminotransferase, a moderate amount of aerobic exercise is the most time-efficient and effective exercise mode.
Yet another view (Arch Intern Med. 2004 Jan 12;164(1):31-9. Effects of the amount of exercise on body weight, body composition, and measures of central obesity: STRRIDE–a randomized controlled study. Slentz CA1, Duscha BD, Johnson JL, Ketchum K, Aiken LB, Samsa GP, Houmard JA, Bales CW, Kraus WE.):
In nondieting, overweight subjects, the controls gained weight, both low-amount exercise groups lost weight and fat, and the high-amount group lost more of each in a dose-response manner. These findings strongly suggest that, absent changes in diet, a higher amount of activity is necessary for weight maintenance and that the positive caloric imbalance observed in the overweight controls is small and can be reversed by a modest amount of exercise. Most individuals can accomplish this by walking 30 minutes every day.
Note none of the results were comparable to the effect on the metabolic syndrome from the Low Carb High Fat diet.