If you’ve been reading fitness magazines for a while — including this one — you’ve seen articles touting 100-rep, aka “century,” sets.
This marathon training technique comes in a couple of flavors, either as an extended drop set where you lower the weight each time you fail as you push to 100 reps, or sticking with the same weight throughout and using brief 10-second rests each time you reach a point you can’t continue.
While the science is scarce, the idea behind century sets is to break through a mental plateau, setting a seemingly impossible goal to help you push yourself further than you normally would. The workload breaks down muscle tissue, setting the stage for the body to repair and grow in response.
Yet, support for this undeniably extreme training style is far from universal among experts. Truth be told, a number of them have called us out for even suggesting it, considering it a waste of time and energy at the very least, and flat-out counterproductive if used beyond the rarest of circumstances.
The Case Against
“While hitting triple-digit reps for an exercise sounds enticing, I would advise against designing your workout around 100-rep sets,” says David Looney, Ph.D., CSCS, an ORISE research fellow at the U.S. Army Institute of Environmental Medicine in Natick, Massachusetts, and an expert in the exercise physiology field. He points to four reasons why:
1. The weight’s just too light. “Your 100-rep max is likely to be at or close to the minimum resistance available for an exercise,” Looney points out, “meaning you will not be stimulating strength, power or muscle gains. In fact, certain exercises can be too difficult to complete 100 reps with even using just your bodyweight.”
2. They unnecessarily ratchet up your injury risk. “A 100-rep set will probably be somewhere around 2-5 times the reps you had previously been training with for an exercise,” Looney explains. “Research has linked drastic increases in training with increased injury risk or excessive muscular breakdown. Imagine what would happen if you tried to do squats with 2 to 5 times your normal squat resistance, or tried to run on a treadmill 2 to 5 times faster than you normally had been?”
3. They force you to leave the best exercises on the shelf. “Fatigue alters your body's normal spatial awareness and can impair your lifting technique over time.,” says Looney. “Highly complex movements — Olympic lifts, squats, deadlifts, etc. — are dangerous to perform with poor technique, and doing that many consecutive reps further increases injury risk.”
In other words, 100-rep sets aren’t well-suited to the best movements — those requiring synergistic action across multiple muscle groups. Instead, in order to get to 100, you’ll likely opt for machine-based exercises and isolation moves. Those have their place in a workout, of course, but are more limited in their overall benefits.
4. They eat up too much time. “A 100-rep set will take you over six minutes to finish if you are lifting in a controlled manner,” Looney says. “That is a fairly sizable chunk of your workout that you’re dedicating to a single set without even factoring in recovery time.” Considering that the exercise is likely an isolation move, at the end of those 100 reps you’ve only hit one area of the muscle group — for instance, if you’ve done incline chest presses for 100 reps, you still have to do sets for your middle and lower pecs for a complete workout.
When to Go Long
So, is there any place at all for 100-rep sets in a typical training regimen? Dan Roberts, CSCS, strength and conditioning coach and founder of The Dan Roberts Group, London, UK, who also typically eschews 100-rep sets, says he did turn to them once in his strength and conditioning career.
“About 20 years ago, I was working with a recently retired pro bodybuilder who was very fast-twitch dominant,” Roberts recalls. “He hired me to help him prep for a circuit training lifting endurance competition, similar to CrossFit. His muscular endurance was terrible, as he had never lifted more than eight reps of anything in his life. We only had eight weeks and I needed to get his mind ready for the pain, build up his lactic acid tolerance, and develop his slow-twitch muscle fibers. We expanded from 20 to 200 reps of everything within a few weeks. And it worked.”
In building up his endurance in a short time, that client did lose a lot of his strength, Roberts points out, but century sets still played a role in him meeting his goal.
Beyond that, if you aren’t in need of a quick endurance boost, you may want to set century sets aside. That doesn’t mean you still can’t reap a couple of key side benefits of the method — that is, helping bust a rut and push yourself past your perceived limits — via other means.
“There are many better ways,” Roberts says. “If it’s purely just pushing through a plateau, then I would try and challenge your body using other more commonly used systems such as negatives, pre-fatiguing, changing the time of your training, doing tri-sets, working with chains, and varying tempos, to name just a few.”
ABC: Always Be Curious
Roberts would recommend a rep range for endurance athletes of 15-20 reps versus century sets if faced with a similar client as his bodybuilder-turned-endurance-competitor again. “The increased stress on muscles and connective tissue, and the mental fatigue you get from an overworked central nervous system, outweigh the benefits,” he admits.
Still, his disinclination to opt for 100-rep sets shouldn’t lead you to dismiss it immediately out of hand. “Having said all this, it’s important to stay open-minded when lifting,” Roberts says. “I don’t want to stop people from experimenting with different techniques. The fun thing about training is when you step into the gym, you have no worries, no restrictions. So maybe give a century set workout a go — just for the experience.”