You're [probably] doing HIIT wrong
Do you want to train for power, strength, and speed? Do you want to look jacked but still be fast and explosive? Then true HIIT [high intensity interval training] is the perfect choice for you.
Unfortunately, HIIT is one of the most butchered training systems out there today. Bootcamp style classes, blank-fit, and other popular circuit training fitness programs claim to be training HIIT when in fact they are probably training MIIT [moderate intensity interval training] or LIIT [low intensity interval training]. While these workouts may feel hard and leave you sweaty, you are actually training submaximally for the duration of the workout and will have submaximal results.
Think of it like this... If I asked you to sprint ALL OUT for 50 meters and you go as hard as humanly possible for you, you could not have possibly ran any faster and harder for that 50 meters, great job. Now we recorded your power output, intensity, and speed for that sprint and document it. Okay, now I am going to ask you to run 800 meters at the exact same intensity and speed that you ran the 50. "That's crazy!? I can't do that!!" Well of course not. While running an 800 meter sprint as hard as possible is definitely gut bustingly difficult, it will never be the same high intensity power output and speed as the 50 meter sprint compared to what your maximal power output and speed potential is. So, if true HIIT is the goal, we have to tailor our training to allow for maximum power output and speed for every single work period and utilize smart rests to recover properly for subsequent efforts to match the first effort.
To understand how and why to properly implement this highly effective training strategy, first we must understand a little about the three energy systems utilized in the body during exercise. While all systems are theoretically active at any given point, it is important to note which is primarily responsible for energy production at various durations of exercise and the overall human performance capable at each point in time.
This is not an energy system, just what we have stored in muscles ready to go. Pretty inefficient, right? We only have 2 seconds worth of ATP stored for maximum performance output, thankfully we have the 3 energy systems available to replenish precious ATP.
ATP-PCR SYSTEM: High Intensity/Short Duration - 8-10 seconds
This is our immediate, high intensity, short burst energy system. The fuel for this system comes from readily available ATP within muscle cells and a small amount of replenishment of used up ADP back to usable ATP thanks to a molecule called phosphocreatine. Our body is able to work maximally, at incredibly high output, utilizing this energy system for about 8-10 seconds. This is an entirely anaerobic process. Once the bout of high intensity work stops; the aerobic system then serves to recover to prepare for another bout of true high intensity exercise. Think of how Usain Bolt trains for his 100 meter sprints. He is concerned about maximum performance each sprint. He sprints hard, recovers for a long time, and goes again. That is HIIT and utilizing the ATP-PCr system primarily during the work periods.
GLYCOLYTIC/LACTIC ACID SYSTEM: Moderate Intensity/Moderate Duration - up to 1 minute
Once the ATP-PCr system has been burned up, our high intensity bout is completed, but our body needs to keep working so we start to tap into stored carbohydrates within our muscles. This stored carbohydrate is called glycogen and we use a series of biochemical reactions to turn glycogen into glucose. We then undergo the process of glycolysis to turn glucose into ATP to fuel muscular contraction. This process is slower, but is still anaerobic and can provide plenty of energy for bouts of exercise at a lower intensity and slightly longer duration than the immediate energy system. Elite level sprinters training 400 meter repeats will utilize this system after the first few steps use up the ATP-PCr system. They will run the 400 in 50-60 seconds, elite level remember, then rest a few minutes to recover aerobically. While for anyone this is definitely high effort, it is still relatively less power output and speed than what that elite level runner would be capable of in the short(er) term.
OXIDATIVE SYSTEM: Low Intensity/Long Duration - 2+ mins continuous effort
Once we have reached the threshold of the ATP-PCr system and Glycolytic system but have not yet rested to recover aerobically, the oxidative or aerobic system kicks into higher gear to provide continuous fuel for muscular contraction and power output. This is a relatively slow process that uses stored fat or other substrates (like proteins) for eventual conversion into ATP. This is our low and slow system, low intensity steady state cardio system. Performance will be low, but it will be sustained. Take our 50m sprint again, imagine holding that speed and power output for a full marathon? Impossible, but thats okay. The oxidative system is there to keep you moving, albeit slower, for 26.2 miles.
How to Train HIIT Properly for Speed and Power
Let's use the chart and what we now know about the energy systems to our advantage to truly train high intensity bouts. The simple prescription is to work as hard as humanly possible for 8-10 seconds. Then recover for 1-2 minutes.
My favorite modalities to accomplish this are low skill movements that we can do basically without thinking.
-Hill or Turf Sprints
-Assault Bike Sprints
-Sled Push Sprints
-Ski Erg Sprints
Pick one, warm up properly [see HOW I WARM UP FOR EVERY TRAINING SESSION], and push through 6-10 maximum intensity bouts with a roughly 1:5 or 1:6 work:rest ratio. This will train you to be more powerful and faster while also improving cardiovascular capacity as you have to recover from each sprint bout aerobically.
Implications for Sport Specific Performance
This could be an entire masters level class but here is the short version...
The average play in American Football is roughly 4-6 seconds making HIIT a great training protocol for athletes in this sport. Most of the time, baseball is the same or even shorter.
But what about basketball? Soccer? Ice hockey? Marathon running? Be a good coach, analyze the sport or activity demands of whoever you are training, and match the training to the energy system that needs to be optimized.
Share this article for any trainers and coaches who need to refine their HIIT approach!