Benefits of Concentric and Eccentric Strength Training What’s the Difference between Concentric and Eccentric Training? Concentric training is most easily thought of as the muscle contraction when a weight is lifted. The muscle fibers shorten while contracting to lift the load as in the upward movement of a bicep curl. An eccentric muscle action is when the muscle fibers lengthen to lower a load, as in the downward movement of a bicep curl. While the fibers are lengthening, they’re also contracting to return the weight to the start position in a controlled manner. Eccentric muscle actions are common in strength training with free weights, body weight exercise, and non-hydraulic exercise machines.