Substrate oxidation during exercise: in type 2 diabetes
Diabetes Metab 2006;32:604-610 • © 2006. Elsevier Masson SAS. Tous droits réservés
. Similarly, an increase in lipid availability causes an
increase in muscular fatty acid oxidation . Hyperglycae-
mia and lipid disorders are frequently associated in T2D
and are both likely to interfere with substrate utilization
with regard to their blood levels. According to our results,
fasting glycaemia before exercise is positively correlated to
COP and PLipoxMax in subjects with T2D.
Many abnormalities are described in the skeletal muscle
of subjects with insulin resistance . However, effects of
insulin resistance on substrate utilization during exercise
have been poorly studied. Previous works are very few,
with too small a number of subjects and were not designed
to delineate the effects of obesity, T2D and insulin resis-
tance by their own on substrate utilization. Once more,
they used only one exercise intensity and cannot establish a
pattern of substrate utilization at various exercise intensi-
Recent guidelines recommend, in T2D, endurance
training, at least 3 times a week, during 45 minutes (inclu-
ding a 5 minutes warm-up) at exercise intensities between
50 and 70% of Wmax [24,25]. These values, used by most
studies referred to in these guidelines, appear to have been
arbitrarily set. There seems to be no clear scientific evi-
dence of a specific efficiency of training at these intensities
rather than others in T2D.
Since the UKPDS, we know that an optimal glycaemic
control with an HbA
<7% is crucial for preventing
microangiopathic and neuropathic complications and
greatly contributes to decrease cardiovascular events in
T2D . If physical activity is used as a specific therapy, it
is mandatory to individualize an exercise intensity aiming
at an optimal glycaemic control and the already proven
benefits on cardiovascular events, other metabolic defects
and general well-being.
Overweight status can contribute to impaired glucose
tolerance and cardiovascular events in T2D. The use of
parameters allowing the individualization of an exercise
intensity at which lipid oxidation is maximal (such as the
PLipoxMax) or at which there is a compromise between
carbohydrate and lipid oxidation (such as the COP) seems
logical. According to a recent study from our group, a
2-months training at the PLipoxMax of subjects with the
metabolic syndrome results in a decrease in BMI, waist cir-
cumference and improves insulin sensibility, lipid oxidation
with an increase in PLipoxmax and COP .
Moreover, efficiency of physical activity on T2D is
dependent on the subject’s long-term adherence to training.
Many factors, specific to the patient or his environment can
explain the lack of adherence. The use of PLipoxmax or
COP as training intensity has two advantages likely to
improve adherence. First, the feeling of the activity as
strenuous or painful can result in training discontinuation.
On the other hand, the intensities proposed by the guide-
lines are particularly high for such subjects cumulating fac-
tors of unconditionning as sedentarity or muscular
abnormalities associated to insulin resistance. As far as
the PLipoxMax and the COP are at lower ranges of values,
the initial intensity of training would make it much easier
to perform. Next, individualizing the training, whatever
the way of choosing intensity, has proven effective for
improving long-term adherence, whatever the behaviour
asked to be changed .
However, improving insulin sensitivity and lipid oxida-
tion is obviously not the only way of improving glycaemic
control and the use of the COP or the PLipoxMax to set
training intensity must prove its efficiency compared to the
guidelines. A randomized controlled prospective study
assessing the short-term and long-term effects of an indi-
vidualized training using the COP, the PLipoxMax or per-
haps another workload individually determined and
compared to a training using the guidelines’ intensities is
necessary. Such a study should also assess the effects on
long-term adherence to individualized training compared
to training based on general theoretical guidelines.
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