There probably isn't an experienced lifter who hasn't come up with the idea of doing some sort of iso-holds between sets in the hopes of getting stronger or bigger. (Basically, contracting or flexing the muscles hard.)
Of course, any lifter who ever tried it probably didn't do it for long because it's hard to keep doing some new technique on faith alone. Too bad they didn't keep it up because, according to one recent study, it looks like it works – at least as far as the quads are concerned.
Granted, a single study does not always a new reality make, but the team that conducted the study included oft-time T Nation contributors Brad Schoenfeld and Bret Contreras.
Both of these guys are PhD types, but almost more importantly, they're also big-time lifters, which isn't always the case with scientists who study these things. As such, the two have important perspectives based on experience and they can devise legitimate training programs to test their hypotheses.
Look at it this way: Dian Fossey and Jane Goodall were damn good gorilla researchers, but they weren't gorillas. As such, they could only guess about what was going through the minds of gorillas. Schoenfeld and Contreras don't face this limitation; they actually are gorillas, so to speak, so their studies carry a lot of legitimacy that might otherwise be lacking.
Anyway, they found that doing 30-second iso-kinetic holds in between sets of back squats and leg presses increased the muscle thickness of the quads. Unfortunately, the results weren't the same for other body parts.
What The Gorillas Did
Schoenfeld and Contreras recruited 35 male lifters from a university population, although 8 of them crapped out before the end of the study for various reasons.
Each training session involved 3 sets of 8-12 reps of the following exercises, each performed with a 1-second concentric (lifting) movement and a 2-second eccentric (lowering) movement:
- Flat barbell press
- Barbell military press
- Wide-grip lat pulldown
- Seated cable row
- Barbell back squat
- Machine leg press
Each lifter did the programs 3 times a week for 8 weeks. The load was subjectively adjusted for each exercise as needed on successive sets and attempts were made to progressively increase the loads each week.
Now here's the rub: The subjects were divided into two groups. The first group rested quietly for 2 minutes between each set of each exercise. The ISO group, however, performed a no-load isometric contraction for the first part of each rest period. They were prodded to squeeze the muscle as hard as possible for 30 seconds and then spend the remaining 90 seconds of the inter-set period resting.
- For the elbow flexors, they tucked their upper arms close to the body and flexed the elbows as far as comfortably possible.
- For the elbow extensors, they kept their upper arms pressed to their sides and extended the elbows as far as possible.
- For the quads, they sat down and extended the legs out straight as if they were performing a leg extension.
What the Gorillas Found
The only muscle that seemed to benefit from the inter-set isometric holds was the mid-thigh area of the quadriceps (which was the only part of the thigh included in their measurements). The ISO group also showed a modest improvement in muscular endurance.
Disappointingly, though, the mid-thigh hypertrophy didn't translate into greater strength increases, but that's often the case – bigger doesn't always mean stronger.
In their conclusion, the researchers wrote the following:
"Those interested in maximizing muscular hypertrophy can consider employing iso-holds in the inter-set period, as this strategy may help to enhance hypertrophy of the quadriceps without increasing total training duration."
How to Use This Info
After doing a set of squats or leg presses, sit down on a bench and extend your lower leg straight out as if you were just completing a concentric rep on a leg extension machine.
Hold the lower leg out there and squeeze the bejesus out of the quad for 30 seconds. Then relax and spend the next 90 seconds counting hairs on your leg before doing the next set of squats or leg presses.
The scientists don't mention whether this technique would work between rest periods of leg exercises other than leg presses and squats, but I think PhD guys like Brad and Bret must swear some kind of oath, probably on the codpiece of Galileo – the father of the scientific method – that prevents them from any extrapolation of their results to include other exercises.
Yeah, yeah. Sure. Fine. But it only makes sense that it would work with any quad movement.
- Brad Schoenfeld, Jozo Grgic, Bret Contreras, Kenneth Delcastillo, Andrew Alto, Cody Haun, Edurado De Souza, and Andrew Vigotsky, "To Flex or Rest: Does Adding No-Load Isometric Actions to the Inter-Set Rest Period in Resistance Training Enhance Muscular Adaptations? A Randomized-Controlled Trial," Front. Physiol., 15 January 2020.