I don't know about that, but you can always counter loss of muscle tone with resistance exercise, vitamins, healthy fats and carbohydrates. Normally loss of muscle tone would be because something that decreases appetite or is catabolic (breaks down tissue and turns it into fat) (like unhealthy fats, too much sugars).
Anti-diabetic effects of puerarin, isolated from Pueraria lobata (Willd.), on streptozotocin-diabetogenic mice through promoting insulin expression and ameliorating metabolic function.
According to the article: "intrapancreatic protein levels of insulin receptor substrate-1 (IRS-1) and insulin-like growth factor-1 (IGF-1) were up-regulated." This would be good for muscle tone, and for anabolism (tissue building).
This: "endogenous mRNA levels of skeletal muscle insulin receptor (InsR) and peroxisome proliferators-activated receptor α (PPARα) were increased after administration of PR" seems to be specific to your question, but I don't understand what that means, except that it relates to muscle tissue by 'skeletal muscle insulin receptor (InsR).
Then it concludes that puerarin increases insulin, and is anti-diabetic, which would be good for muscle maintenance.
On the other hand, many chemicals that increase sensitivity of receptors, also cause that receptor to lower its activity for now. While this is usually true, taking too much of something that increases sensitivity, while temporarily lowers its activity can damage that receptor (doing the opposite which is decreasing sensitivity).
If you're worried about puerara mirifica's effects on muscle tone, limit its dose, alternate it, and time its use to get better effects. Where did you see that it does that?