High intensity training gets all the love. And for good reason—it’s tough, it’s time efficient, and it works. Low intensity training is a less appreciated form of conditioning, yet can have tremendous impact on athletes that participate in sports and depend on repeated, explosive bursts of speed such as football, soccer, and hockey.
It’s counterintuitive to think that going for an easy jog or bike ride would be of any use to an athlete who depends on speed for success. In fact, when I started out as a strength and conditioning coach (back in 2009), it was popular for coaches to bash low intensity training, feeling it wasn’t specific enough to the sports their athletes were training for.
But the specificity argument only goes so far. If being specific was the primary goal of training, no one would be lifting weights. After all, not too many athletes have to compete with metal bars balancing on their shoulders. But no one advocates for putting down the iron because they recognize the value that strength training has in sports performance.
When considering a new training option, we should be asking ourselves, “What’s the value this brings to the athlete?” Not, “How specific is this to the sport?”
Low Intensity Training, Defined
Low intensity training goes by many names: steady-state cardio, long slow distance, and submaximal exercise to name a few. But I prefer the term “low intensity” because I think it most accurately describes the nature of the training. It has nothing to do with pace, speed, or duration—those are all byproducts of an athlete’s fitness. It’s the level of intensity, or effort, that produces the effect we’re looking for.
So how low is low? Published research on the topic suggests 70% of one’s max heart rate.1 But in my experience, the optimal heart rate for low intensity training varies tremendously by individual. Not only is max heart rate itself highly variable between athletes, but so is training status, age, and resting heart rate—all of which influence an athlete’s target heart rate zone. For example, my sweet spot is between 135-140 beats per minute when running. But I’ve coached athletes that could cruise along at 165 (which would set my lungs on fire) and look like they could take a nap.
At the end of the day, low intensity training should feel easy, which can be a big mental shift for athletes used to grinding and pushing their way through torturous high intensity interval sessions. When doing low intensity exercise correctly, athletes should be able to carry on a normal conversation or breathe easily through their nose. In other words, the training should not impact respiration too much. What I tell my athletes is, “When your breathing deepens and it starts to feel like effort, take it down a small notch.”
A lot of athletes I work with are uncomfortable training at such a low effort. Since they don’t get tired, they mistakenly (but understandably) feel that not much is happening. But that’s usually a sign that they’re doing it right.2
The Body’s Response to Low Intensity
Low intensity training develops the aerobic system, which uses stored body fat as well as oxygen to meet the majority of the body’s energy needs. Although it can’t produce energy quickly, the aerobic system is very efficient, and can provide a steady supply of fuel for hours at a time.
There are a number of aerobic adaptations that occur as a result of low-intensity training. The heart responds by increasing the strength of its contractions as well as its overall size, allowing more blood to be pumped with each beat and resulting in greater overall efficiency. This is why one of the hallmark signs of an improving aerobic system is a drop in resting heart rate—the heart just doesn’t have to work as hard to deliver oxygen to the body.
There are also changes that happen to the muscles themselves. Additional capillary beds, the smallest branches of the circulatory system, get created near the working muscles and allow more oxygen-rich blood to reach them. Individual muscle cells also generate more mitochondria and aerobic enzymes, both of which improve the rate at which they can produce energy aerobically.3
The Value for High Intensity Athletes
A healthy, robust aerobic system is something that all people, regardless of whether they’re an athlete or not, strive to achieve. But the biggest benefit for an athlete is improved recovery from high intensity activity. Athletes with better aerobic energy systems are simply able to absorb and recover from more intense efforts faster and easier than others.
As part of my assessment protocol with athletes, I often have them ramp their heart rate up as high as possible through short, repeated sprints, and then monitor them for a few minutes after they finish. An athlete with a well-developed aerobic system will get their heart rate back down to a comfortable 130-140 beats per minute after 60-seconds of hitting their max, whereas poorly conditioned athletes are still huffing and puffing with their heart rate jacked up into the 160s.
An athlete’s inability to quickly recover means a heavier dependence on their anaerobic system for energy. The anaerobic system can generate a lot of energy in a short amount of time, but produces a ton of muscular damage and metabolic waste when used too much, making it difficult to recover from.
Few sports demand just a single explosive effort. Most depend on an athlete’s ability to be explosive repeatedly. A better aerobic system means less anaerobic activity is required to produce energy, resulting in a fresher, more effective athlete in the later stages of competition.
The Role of HIIT
At this point, the high intensity interval training (HIIT) crowd is probably saying, “Wait a second, I heard that HIIT is actually better for developing the aerobic system. What gives?”
This, to a degree, is true. Research consistently shows that HIIT does a better job of improving markers of aerobic fitness compared to low intensity exercise over the course of 6 to 12 weeks.1, 4 So if an athlete can get more benefit from a few 30-second sprints than they can with a 45-minute jog, going with a pure HIIT approach seems like a no-brainer, right?
But just because something plays out a certain way in the laboratory, doesn’t always mean it’s the best training decision in the real world. What we don’t see from these studies is the cost that these two training styles take on the body.
Where Low Intensity Training Shines
HIIT requires violent, maximal efforts that produce a ton of muscular damage and central nervous system fatigue. It’s not uncommon for an athlete to need several days to fully recover from one HIIT session. Low intensity training, on the other hand, should be gentle, rhythmic, and easy on the body. By keeping the heart rate low, the athlete never gets to the point where they’re exerting themselves too much. They finish sessions feeling relaxed and restored, with little to no fatigue the following day. It’s this difference that makes low intensity training such a useful tool for me as a coach.
Most of the athletes I work with have very demanding schedules. And while a HIIT workout might seem like a perfect fit for the time-crunched athlete, it only makes sense if the athlete is rested enough to put in a quality effort and has ample time to recover. Adding intensity to an overstressed athlete is a recipe for burnout and injury.
Designing a training program is as much about stress management as it is anything else. Unlike HIIT, the gentle nature of low intensity training means it can be placed almost anywhere in an athlete’s weekly plan, making it a highly adaptable way to develop the aerobic system that doesn’t stress the athlete.
Many of the athletes I introduce to low intensity training, while initially skeptical, are shocked at how much better they feel when they finish a session. Over time, they actually learn to welcome the change of pace and see it as an opportunity to unwind and relieve some stress. It’s got a very powerful effect on the nervous system and is a fantastic way to facilitate recovery.5, 6
Find a Place for Low Intensity Training
Specificity still matters, let’s not forget that. It’s important that athletes are training in a way that will prepare them for the specific demands of their sport, and HIIT must be a part of that strategy.
But low intensity training still has a place for the high intensity athlete. Not only will it build a strong, aerobic engine that supports and improves recovery from more intense efforts, but it does so in a way that’s restorative and gentle on the body, allowing the athlete to recover and come ready to hit the gas the next day.
That, for me, is a double win and tremendous value is added for the athletes I coach.
1. Jan Helgerud, Kjetill Hoydal, Eivind Wang, Trine Karlsen, Palr Berg, Marius Bjerkaas, Thomas Simonsen, Cecilies Helgesen, Ninal Hjorth, Ragnhild Bach, and Jan Hoff. “Aerobic High-Intensity Intervals Improve VO2max More Than Moderate Training.” Medicine & Science in Sports & Exercise 39, no. 4 (April 2007): 665-71. doi:10.1249/mss.0b013e3180304570.
2. Livingstone, Keith. Healthy intelligent training: the proven principles of Arthur Lydiard. Maidenhead: Meyer & Meyer Sport, 2012.
3. Joyner, Michael J., and Edward F. Coyle. “Endurance exercise performance: the physiology of champions.” The Journal of Physiology. 586, no. 1 (September 01, 2008): 35-44. doi:10.1113/jphysiol.2007.143834.
4. Ramos, Joyce S., Lance C. Dalleck, Arnt Erik Tjonna, Kassia S. Beetham, and Jeff S. Coombes. “The Impact of High-Intensity Interval Training Versus Moderate-Intensity Continuous Training on Vascular Function: a Systematic Review and Meta-Analysis.” Sports Medicine. 45, no. 5 (May 15, 2015): 679-92. doi:10.1007/s40279-015-0321-z.
5. K. Tian, J. Qin, L. Huang, M. Long, J. Wu, S. Yu, and Y. Yu. “The effect of aerobic and anaerobic endurance training on the regulating function of autonomic nervous system and its significance.” Journal of Biomedical Engineering. 23, no. 5 (October 2006): 1020-023.
6. Stanley, Jamie, Jonathan M. Peake, and Martin Buchheit. “Cardiac Parasympathetic Reactivation Following Exercise: Implications for Training Prescription.” Sports Medicine. 43, no. 12 (August 03, 2013): 1259-277. doi:10.1007/s40279-013-0083-4.