Slow Twitch, Fast Gains

Fast-twitch fibers may get all the attention, but the strategic targeting of your slow-twitch muscle fibers can help maximize growth.

Science has come a long way in the world of strength and hypertrophy training, but there’s a problem. The way we humans are, it’s easy to dive headlong into the newest, shiniest fitness trend, product or research item. That’s not always a bad thing; solid science is hard to argue with. And in the case of targeting different muscle fiber types, we’ve been conditioned to focus on our fast-twitch fibers because of the role they play in getting us bigger and stronger. That’s fine, but as a result we’ve marginalized the usefulness of our slow-twitch muscle fibers and their related energy systems.

Training methods that use extended sets to push you past failure have those sets last longer than 10 to 15 seconds. In some cases, much longer. The reason these methods work so well is that they completely exhaust muscle tissue and make even the lightest weight feel heavy. That shift in the rate of perceived exertion is really the key player when it comes to making muscles grow; it’s even more important than the absolute percentage of your one-rep max. The common thread with these approaches? They’re all dominated by slow-twitch muscle fibers.

See, the truth is, the slow-twitch muscle fibers are involved before, during and after any set that you do. Muscles geared for posture and stability that may be anchoring points for holding weights are contracting the entire time. So it’s not worthwhile for any athlete to completely neglect those muscle fibers in pursuit of hitting only the fast-twitch variety. Any complete program targets multiple types of muscle fibers. Here are two ways to do it right.

1. Modify Tempo + Increase Time Under Tension

Increasing your muscular time under tension can easily be done by making a standard set of, say, 10 reps last much longer. Explode upward the way you normally would to emphasize fast-twitch muscle fibers, then on the way down control your rep for a three- to four-second negative. This will make the muscle work harder and continue doing so once the fast-twitch fibers have dropped out of the lift at about the 15-second mark when your explosive energy stores expire. At this point, your slow-twitch fibers will have to augment their contribution to each repetition. It’ll make for a much more difficult set, and chances are you’ll have to reduce your working weight by 10 to 20 percent.

2. Know Thy Muscle Groups

Certain muscles or regions of the body will most definitely contain a higher proportion of slow-twitch muscle fibers simply due to their role. Slow-twitch muscles don’t fatigue as quickly and are geared toward endurance and postural functions, so it’s fair to say that muscles of the back, calves, quads and upper arms may respond better to high-rep training. With this in mind, you won’t get too far working with sets of six to eight reps on the seated row; sets of 15 reps are a better fit.