The Future of Strength Training

Army researchers assess the evidence on what makes you stronger, and speculate about new approaches that might work even better

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Getting stronger is simple: lift heavy stuff, put it down, and repeat. According to a new review led by researchers from the U.S. Army Research Institute of Environmental Medicine, you should use heavy weights that you’re capable of lifting one to five times through a full range of motion, and repeat for two to three sets a few times a week. That's it. The rest is details.

Of course, the details are sometimes interesting—especially if you’re really trying to max out your performance, or returning from injury, or deployed somewhere far from the nearest gym. That's what motivated the new review paper, which is published in the Journal of Strength and Conditioning Research by a team led by Barry Spiering, who was at USARIEM but has since moved on to a position as lead physiologist at New Balance's Sports Research Lab. He and his colleagues tried to sum up what we currently know about how to get stronger in order to imagine how we might do better.

The opening section digs into root causes: what has to happen in your body in order to increase strength? Surprisingly, the first thing they identify is giving maximal mental effort. The bigger and clearer the signal your brain sends to your muscles, the more force you’ll produce. And that signal-sending capability is trainable. Back in 2021, I wrote about a fascinating study in which locked-down pro basketball players gained strength by doing six weeks of completely imagined strength workouts three times a week. Similarly, lifting a light weight while imagining that you’re lifting a heavier one—i.e. trying as hard as you can, even if you don't need to—produces greater strength gains.

Of course, strength isn't all in your head. At the other end of the spectrum, using electricity to stimulate forceful muscle contractions also leads to strength gains, even though that requires no mental effort at all. In this case, it's the muscle fibers and neurons themselves that adapt. So a training program that's both mentally and physically challenging is the best of both worlds. Spiering also argues, based on the literature, that exercises should include both lifting and lowering the weight, and should move through a full range of motion.

The final point is more controversial: does metabolic stress in the muscles trigger strength gains? Endurance athletes know that hard exercise triggers a rise in lactate in their muscles, but that's just one example among many: by one count, at least 196 metabolites rise or fall after a workout. One line of evidence that metabolites matter: blood-flow restriction training, which involves putting a blood-pressure cuff on your arm or leg while you lift, traps those metabolites in the limb and enhances the response to what would otherwise be easy exercises. Not everyone is convinced that metabolites matter for strength, but it's an area of active research.

Given what we know about how to stimulate strength gains, Spiering and his colleagues spitball some ideas for how to move beyond the usual lifting of heavy stuff.

One option is to lift heavier-than-maximal weights. This might seem impossible by definition, but there are a few possible workarounds. You could use electrical stimulation, either of the brain or of the nerves that activate the muscles themselves, to squeeze a little extra out of your muscles when you’re already pushing as hard as you can. You could take advantage of the fact that you can generate more force eccentrically (when you’re lowering a weight) than concentrically (when you’re raising it) by rigging up a system that gives you a heavier weight on the way down than the way up.

You could also figure out ways of amping up your mental effort during a lift that's already at your physical limit. The weight itself isn't heavier-than-max, but the neural effort—and perhaps the resulting adaptations and strength gains—are. Alternatively, you could use mental imagery to add supplementary (but imaginary) workouts between your physical workouts, without delaying your muscles’ recovery from the last workout.

Biofeedback is another hot topic. Wireless EEG electrodes can quantify how hard your muscles are working, and show you the data on your phone in real time. This could help you push harder, or keep your effort in a target zone. Other technologies like muscle oxygen sensors could finetune when to stop one set, or when you’re recovered enough to start the next set.

Based on the ideas above, Spiering and his colleagues suggest a three-tiered approach to deal with specific strength-training challenges.

The first tier is no-load training, which is most relevant if you’re rehabbing an injury that prevents you from doing any physical training at all. One example, as mentioned above, is mental imagery workouts, where you imagine lifting weights in as much detail as possible. Another is opposite-limb training: if you have surgery on your left leg, you do exercises with your right leg. Since the brain signals for both limbs run along the same pathways, you get a "cross-education" effect that partly maintains strength in the injured limb. Finally, blood flow restriction might help, perhaps by elevating metabolic stress, even if you’re unable to train the limb.

The second is low-load training, which again could be useful during injury rehab and also works well if you don't have access to a lot of gym equipment. There's a robust body of evidence that lifting light weights can produce similar strength gains to lifting heavy weights, with the key caveat that you need to lift until close to failure. In other words, you need low load but high effort. There may be other ways of getting this effect, like the study mentioned above where subjects lifted a light weight but imagined they were lifting a heavier one.

Finally, there's the broad category of "supplementary activities": biofeedback based on EMG or other data; electrical stimulation; blood flow restriction. All have been the subject of promising research, but none is quite ready to be rolled out for general consumption with simple guidelines.

The takeaway? I still think the basics of strength training are straightforward. For most of us, in most situations, it's probably a good idea not to overcomplicate it: lift heavy stuff and don't worry about imaginary exercises or electroshock workouts. But the ideas above are worth remembering for situations where, for one reason or another, you can't do a normal workout. And the one insight I’ll keep in mind for all my workouts is the importance of mental effort. I’ve always felt this intuitively, but it's nice to know that being present and trying your hardest, rather than letting your mind wander, is a research-backed path to greater strength.

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