Over roughly 250 years, therapeutic electrical stimulation has jumped to a new level perhaps seven times, and each jump was made possible by a new technological development. It might have been a way of handling current, storing it, generating it, shaping it, measuring it, timing it, or using it to tune the nervous system rather than drive it, and finally today triggering it from the person's own movement or intention. These are the stages I allude to in the title.

The first stimulator I worked with, as a PhD student in the late 1970s, filled a good part of a laboratory bench and needed someone who understood it standing beside it. The Stim2Go electrical stimulation device I carry to homes or clinics now is the size of my hand. It can be strapped to a client's thigh, senses when they start to move, and is set up from an app on my phone. Both deliver a pulse of current to a nerve. Almost everything else about them has changed.

It is quite common for us to meet clients who have tried electrical stimulation on a limb and found that nothing happened. No matter how high the intensity was set, the muscle simply would not contract. They arrive frustrated, sometimes having been told that nothing more can be done. When we then use the RISE Stimulator, a specialist device capable of producing the long-impulse-duration waveforms that denervated muscle actually requires, they are often surprised and relieved to see a contraction for the first time.

That moment of surprise reveals an important gap in understanding. The muscle did not fail to respond because it was beyond help. It failed because the wrong electrical 'language' was being spoken. A denervated muscle is not simply a weak muscle. It is, in a very real sense, a different tissue with altered structure, electrical properties, and activation rules. Understanding these differences is the foundation for making sense of any treatment approach.

Electrical stimulation is a popular and widely used approach for physical rehabilitation. When used for muscle strengthening, it is necessary to take into account the fact that electrical stimulation produces muscle contractions in a relatively inefficient way.

In this article, we take a brief look at muscle fibre types. Following a neurological insult, muscle fibre types undergo transformation, producing changes that affect the ability of muscles to do work. We examine the particular case of spinal cord injury and consider how this affects the effectiveness of electrical stimulation.

Approaches to combat fatigue are examined. Finally, we consider attempts being made to improve the performance of stimulators and produce consistent muscle contractions under all circumstances.

Electrical stimulation can be an effective way to strengthen skeletal muscle, but outcomes depend heavily on how it’s applied. This article explores what the research suggests about effectiveness, and which stimulation parameters appear most important - such as intensity, frequency, pulse duration, and session length. It highlights why correct dosing and progression matter, and how stimulation can be tailored to support different strength and rehabilitation goals. A useful overview for clinicians and individuals looking to understand evidence-based stimulation for muscle strengthening.