Maybe reductionist and oversimplifying, but what about just relatively large amounts of cardio during offseason? Can that offset some of the gh induced insulin resistance.
Not really, honestly. Bodybuilding-style resistance training is really the ideal means to stress the glycolytic system, and use glucose as an energy substrate to perform work (characterized by short rest intervals between repetitions [with load] that last 30 sec - 1 min); you might characterize that as something approaching glycogen depletion training or anaerobic capacity work. This directly lowers blood glucose, but is not insulin sensitizing.
While zone 2 cardio in particular improves mitochondrial function, which in turn enhances insulin sensitivity, it primarily increases CPT1/carnitine system transporter function (a fatty acid transporter), this is primarily a local adaptation (albeit in skeletal muscle, which constitutes a majority of our tissue) as opposed to the GLP-1 & GIP agonists acting centrally to enhance insulin sensitivity.
We really need centrally-acting insulin sensitizing agents (e.g., GLP-1 & GIP agonists) to counteract more potent drug effects, that are not attached to cardiovascular fitness.
That is to say, the effect of cardio will be modest at best.
I generally see a lot of the chatter promoting cardio to enhance longevity in enhanced bodybuilders as wishful thinking, it could even be construed as magical thinking.
Given that GH induces insulin resistance by increasing circulating FFAs, by acting to enhance HSL activity, increased CPT1 & mitochondrial function really won't serve the task of ameliorating this action of GH (moreover, cardio stimulates HSL).
Slin is like throwing fuel on the fire of rhGH's insulin resistance, in progression to T2DM, given that it induces:
1. central obesity
2. elevated triglycerides; ↓HDL, ↑Apo B, ↓Apo A1 (dyslipidemia)
3. endothelial dysfunction (altered arterial tone ⇒ atherosclerosis)
4. atherosclerosis (factors: platelet adhesion, aggregation, thrombogenecity ⇒ inflammation)
5. hypertension
6. prothrombotic activity
Slin further stimulates VLDL secretion in the liver and
directly worsens insulin resistance (as HOMA-IR is a function of blood glucose
and blood insulin levels).
AAS induce left ventricular hypertrophy and diastolic function derangement directly. Combined rhGH+AAS quite dramatically increases cardiomyopathy. RhGH directly alters cardiovascular function, induces LVH, etc.
No volume of cardio does anything to ameliorate these direct drug effects.
The sole benefit, as I see it, of cardio for enhanced bodybuilders per se, is by reducing the resistance training-induced increase in arterial stiffness.