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Muscles can’t be confused. They can only contract or not. Everything else is marketing.
“The only way to give the muscles greater stimulation is to administer greater amounts of mechanical loading. And the only way to get that is to keep on the same movement, get better and better at it, and handle heavier and heavier resistance.” — Jim Keen, Director of Training at FastFit®
If you’ve ever felt like you need to constantly switch up your workouts to keep seeing results, this episode is for you. Jim Keen and I take on one of the most persistent myths in fitness: muscle confusion.
We trace the term back to the P90X era—the idea that you had to “shock” and “surprise” your muscles to force growth. The problem? Muscles don’t have personalities. They can’t be confused. A muscle fiber has exactly two states: active or inactive. So what was actually happening when people saw results from a new workout? Motor learning. When you start any new movement, most of your early improvement is neurological—your nervous system getting more efficient at the skill. Switching to a new movement just restarts that curve: you get weak, then improve rapidly again. It feels like progress, but you’re retracing old ground back to where you already were. The muscle never received greater stimulation.
The only way to actually grow is progressively greater mechanical loading on the same movement.
Then we discuss workout variety. The key distinction: variety is genuinely required with weights, but not with isokinetic resistance technology. With a barbell bench press, no muscle group works at 100% intensity, so you need incline, decline, flies, and crossovers to hit every fiber. Jim used this analogy: it’s like one person walking a bunch of dogs—a weight only pulls the dogs necessary to move it. On a FastFit® machine, you pull and all the dogs move. Every recruitable fiber is maximally stimulated in a single movement, so one chest press smokes the whole chest and front delt.
The proof is the Western Colorado University study. Over 12 weeks, the weightlifting group did ten movements; the FastFit® group did six. Yet the one-rep and five-rep max gains for the FastFit® group were roughly double the weightlifting group—even on lifts FastFit® never trained. The weightlifters practiced overhead press for 12 weeks; the FastFit® cohort never went overhead and still beat them. The FastFit® users even doubled their hamstring curl gains without doing a single leg flexion.
The takeaway: less variety and less time is a feature, not a bug. FastFit® still offers plenty of variety: 17 movements, 5 protocols, 3 pathways. You’re not missing anything. But the weight-room level of variety simply isn’t necessary. More isn’t better. Better is better.
In this episode, you’ll learn:
- Where the idea of “muscle confusion” came from and why muscles literally cannot be confused
- Why switching exercises to beat a plateau just retraces old ground instead of adding stimulus
- The real way to grow: progressively greater mechanical loading on the same movement
- Why variety is genuinely required with weights but unnecessary with isokinetic resistance exercise
- The Western Colorado University study: how FastFit® beat weightlifters at movements they never trained on
- Why less variety and less time is a feature, not a bug—and why more is not always better
🎧 Listen to the episode now:
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