This is an interesting idea which in some ways seems to confirm an intuitive conclusion – you see labourers with fat bellies and muscular arms; joggers with lean legs and fat arms – but I do not think that the general prescription should be changed to spot reducing.
The key is how much total energy is being expended, how many calories are burnt. Leg extensions, crunches or whatever will not burn much energy. To achieve that you will have to be bit more active: sprints, jumps, squats, chins, presses. These take energy and will burn fat from all over. It is about proportions. For example, crunches might burn a high percentage of calories from the abs....but not many overall, whereas squats might not burn a high percentage of calories from the abs...but loads in total. So, do you want to burn 100 calories with 70 from the abs (70%) or maybe 500 with 150 (30%) from the abs? It is easy - do the exercises that burn the most in total....
Are blood flow and lipolysis in subcutaneous adipose tissue influenced by contractions in adjacent muscles in humans?
Bente Stallknecht, Flemming Dela, and Jørn Wulff Helge
Department of Medical Physiology, The Copenhagen Muscle Research Centre, The Panum Institute, University of Copenhagen, Copenhagen, Denmark
Submitted 5 May 2006 ; accepted in final form 11 September 2006
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 (Wmax) for 30 min followed by exercise at 55% Wmax for 120 min with the other leg and finally exercised at 85% Wmax for 30 min with the first leg. Subjects rested for 30 min between exercise periods. Femoral SCAT blood flow was estimated from washout of 133Xe, 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% Wmax 6.6 ± 1.0 vs. 3.9 ± 0.8 ml·100 g–1·min–1, P < 0.05; 55% Wmax 7.3 ± 0.6 vs. 5.0 ± 0.6 ml·100 g–1·min–1, P < 0.05; 85% Wmax 6.6 ± 1.3 vs. 5.9 ± 0.7 ml·100 g–1·min–1, P > 0.05; lipolysis: 25% Wmax 102 ± 19 vs. 55 ± 14 nmol·100 g–1·min–1, P = 0.06; 55% Wmax 86 ± 11 vs. 50 ± 20 nmol·100 g–1·min–1, P > 0.05; 85% Wmax 88 ± 31 vs. –9 ± 25 nmol·100 g–1·min–1, P < 0.05). In conclusion, blood flow and 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.