It is well-known that heavy loads produce greater strength gains, compared to training with light or moderate loads.

Heavy loads probably achieve these greater gains in strength by:

  • ↑ increases in neural drive
  • ↑ improvements in coordination
  • ↑ increases in the specific tension of the muscle itself (muscle quality)

More recently, studies have emerged showing that heavy loads also produce greater gains in rate of force development (RFD), in comparison with light or even moderate loads.

Surprisingly, training with heavy loads seem to be even better for improving RFD, than for improving strength!

Strangely, however, although it involves heavier loads, eccentric-only training is not better for improving RFD than concentric-only training.

In fact, concentric-only training may be slightly superior.

Why is this?

Well, the superior improvements in RFD after heavy load strength training could occur because of increases in muscle-tendon stiffness (training with heavy loads is known to produce greater increases in tendon stiffness than training with lighter loads).

Stiffer muscle-tendon units start applying force to a joint sooner than less stiff muscle-tendon units, as a muscle begins contracting. Therefore, stiffer muscle-tendon units tend to display faster RFD.

And while concentric-only and stretch-shortening cycle training increase muscle-tendon stiffness, eccentric-only training does not. This is because eccentric-only actually reduces muscle stiffness, perhaps because it increases muscle fascicle lengths very effectively.

So while eccentric-only training is a great method for preparing athletes for sport and reducing injury risk, it may need to be balanced by other methods as well. After all, RFD is a very important athletic quality.