Research Watch

Reference
Stallknecht B, Dela F, Helge JW. Are blood flow and lipolysis in subcutaneous adipose tissue influenced by contractions in adjacent muscles in humans? Am J Physiol Endocrinol Metab. 2007;292:E394-E399

Abstract
Aerobic exercise increases whole body adipose tissue lipolysis, but is lipolysis higher in subcutaneous adipose tissue (SCAT) adjacent to contracting muscles than in SCAT adjacent to resting muscles? Ten healthy, overnight-fasted males performed one-legged knee extension exercise at 25% of maximal workload (W(max)) for 30 min followed by exercise at 55% W(max) for 120 min with the other leg and finally exercised at 85% W(max) for 30 min with the first leg. Subjects rested for 30 min between exercise periods. Femoral SCAT blood flow was estimated from washout of (133)Xe, and lipolysis was calculated from femoral SCAT interstitial and arterial glycerol concentrations and blood flow. In general, blood flow and lipolysis were higher in femoral SCAT adjacent to contracting than adjacent to resting muscle (time 15-30 min; blood flow: 25% W(max) 6.6 +/- 1.0 vs. 3.9 +/- 0.8 ml.100 g(-1).min(-1), P <> 0.05; lipolysis: 25% W(max) 102 +/- 19 vs. 55 +/- 14 nmol.100 g(-1).min(-1), P = 0.06; 55% W(max) 86 +/- 11 vs. 50 +/- 20 nmol.100 g(-1).min(-1), P > 0.05; 85% W(max) 88 +/- 31 vs. -9 +/- 25 nmol.100 g(-1).min(-1), P < class="blsp-spelling-error" id="SPELLING_ERROR_11" onclick="BLOG_clickHandler(this)">lipolysis are generally higher in SCAT adjacent to contracting than adjacent to resting muscle irrespective of exercise intensity. Thus specific exercises can induce "spot lipolysis" in adipose tissue.

My Thoughts
This piece of research was pre-published a few months back, and on the surface appears to support the concept of spot reduction. However, taking a slightly deeper look into the paper reveals the difference between statistical and clinical significance.

At the end of the discussion, the authors translate the difference in lipolysis to

"Assuming a molecular weight of 860 g/mol for TG, this corresponds to an extra breakdown of 0.6 –2.1 mg of TG in 30 min/100 g of adipose tissue adjacent to contracting muscles.."

So to lyse 1gram of additional fatty acid per 100gram of adipose would take

0.6mg/30mins = 1.2mg/hour
1000mg/1.2mg/hour = 833 hours of relatively intense activity

or

2.1mg/30mis = 4.2mg/hours
1000mg/4.2mg/hour = 238 hours of relatively intense activity

Sure we can measure it and show a significance difference, but what point is the difference of 1.2-4.2mg/hour/100g fat?