High-intensity interval training is considered by many to be the Holy Grail of exercise. It promises unmatched conditioning and fat-loss benefits in minimal time, causing it to skyrocket as one of the most popular styles of training. If you're not familiar, read our Complete Guide to HIIT Training.
But like any popular trend, it can be taken too far.
We see folks integrating HIIT into as many of their workouts as possible. They HIIT for conditioning. They HIIT for strength. They HIIT while they eat. They HIIT while they sleep.
OK, the last two aren't true. But you get the point. HIIT is everywhere.
If you're trying to lose weight or improve conditioning, frequent HIIT-ing won't pose much of a problem. But if strength is your goal, you need to be careful.
A recent study from the College of New Jersey assessed how aerobic exercise, including HIIT-style workouts, affect a subsequent strength training workout.
We've known for a long time that cardio and strength workouts don't pair well together—especially if you do cardio beforehand. Fatigue, the type of muscle fibers trained and other changes caused by aerobic exercise have consistently shown in research to decrease strength performance.
HIIT-style workouts appear to pose an even bigger problem. The researchers found that after a HIIT workout, reps and power on strength exercises took the biggest hit (pun totally intended) compared to three other steady-state cardio workouts—even though the HIIT workout was up to 40 minutes shorter than the aerobic workouts.
The researchers point to the intensity of HIIT workouts. To be effective, you must work at or near your max. Although they're shorter in duration, HIIT workouts induce significant fatigue, making it virtually impossible to perform strength exercises at your full capacity afterwards.
The result is a poor quality workout. You might feel like the workout is difficult, but you're not challenging your muscles in a way that causes strength and power improvements.
We don't see a ton of people doing HIIT before strength workouts. Mostly, it's done as a workout finisher, which is perfectly fine from time to time.
However, we do see HIIT and strength workouts mixed together. You might feel like you're killing two birds with one stone when in reality you are getting a half-assed version of both.
This serves as an important lesson when training: Always have your goals in mind.
If your goal is to get stronger, then lift some freakin' weight. If you want to improve your conditioning and lose fat, then do HIIT.
Yes, there's some crossover. You can do strength one day and HIIT another. Or as mentioned before, you can do a quick HIIT finisher at the end of a strength workout. But doing HIIT before a strength workout or mixing the two are not ideal strategies for crushing your lifting goals.
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