Intervals

by Dr. Daniel Shaye, Chiropractic Physician

In many areas of the country, Club runners often assemble weekly for Interval Day. What are Intervals? What is their purpose? How does your body respond to them?

Intervals refer to a series of hard efforts, interspersed with rest. You can run them on a track, or around a field, or even around the block. The hard efforts are typically run at a pace that is uncomfortable, but sub-maximal. If you can’t sustain the pace of your initial efforts (i.e. you run your first hard lap in 92 seconds, your second in 93, your third in 1:45, and end up jogging the last repeats), you’ve overwhelmed your body’s current ability to handle the effort. Interval training is all about training to run distance efficiently and wisely, within your body’s capacity, but repeatedly nudging up against and expanding your body’s limits.

Resting periods—typically taken up by walking or slow running—should be long enough to allow another hard effort, but not so long as to allow full recovery. The “interval” is NOT the hard effort; instead, the “interval” is the recovery period between the harder running. Shorter rests mean less recovery, and a stronger training effect as the aerobic system is forced to recover more quickly.

Let’s say we have a 5000 meter runner whose goal is 18:00. He or she may choose to run a variety of distances on interval days, but one core workout might be 5 x 1000 meters. Initially, the runner may cover these repeats in 3:45 (18:45 5K pace) with 400m (roughly 2 ½ - 3 minutes) jog recovery. Eventually, this athlete will be able to run the same workout with less rest—say, with 200m (roughly 1 ½ - 2 minutes) jog recovery. This athlete is closer to the goal, because his or her ability to recover is improving. Over time, he or she is likely to adapt, lowering the average kilometer for this workout to 3:30, despite the shorter rest intervals. This athlete is ready for a breakthrough race in the form of 5 x 1000 meters at 3:36 per 1000m, with zero rest… i.e. an 18:00 5K.

Physiologically, the body responds to interval training in a variety of ways. Your very bones change and become denser, stronger, in response to stress. Other systems the runner or fast/competitive walker trains include lungs and heart (“cardiopulmonary system”), peripheral vascular system (arteries, capillaries, and friends), central nervous system (brain, spinal cord), peripheral nervous system (nerves to working muscles), and skeletal muscles themselves… all the way down to the cellular level.

VO2max is the body’s maximum ability to uptake and use oxygen. The higher your VO2max, the more oxygen your lungs can absorb and efficiently deliver to aerobically exercising skeletal muscles before you hit your limits. The lungs and heart are a critical team when it comes to VO2max, with the former absorbing oxygen and expelling waste gas (CO2), and the latter pumping the oxygen-rich blood to the skeletal muscles while simultaneously circulating the waste-product-laden “used” blood through the lungs so they can expel CO2. And did you know that runners can literally add miles of blood vessels to their bodies, in response to healthy aerobic stress?

A high VO2max is essential to endurance performance, but NOT sufficient. There are athletes with world-class VO2max who do not move efficiently; and they fail to reach their potential, get injured, or both. You need to train your nervous system to coordinate the movement of well-functioning parts. The key is not to imagine the body as a heart-lung team, or a set of legs, or a bunch of nerves trying to coordinate an agglomeration of functions; rather, the body functions best when all the components work together, efficiently. That tight hip, that lack of endurance, that worn out shoe… these are things doctors and coaches and others can help you with. Then there’s the matter of becoming self-aware, of realizing you get less knee lift when you’re fatigued, or tighten your face and shoulders, or stop pushing off powerfully. That’s central nervous system training: integrating all the signals, training the body to hold optimal form despite pain and fatigue, and training the mind (soul?) to believe that despite the terrifying jaws of aerobic debt, self-doubt, and looming aerobic limits, that the limits you are exploring are also limits of belief, self-imposed limits. Every race, every run, every interval session can be about exploring a bunch of body parts and systems, or it can be about exploring possibility. Perhaps you can explore both, and come out a better runner and more self-aware person.

I'll see you on the roads and trails, my friends.

-Dr. Daniel A. Shaye

Certified Chiropractic Sports Physician
Fellow, International Academy of Medical Acupuncture

Do you have a question you’d like answered? Mail your questions c/o Performance Chiropractic, 1307 Jamestown Road, Ste. 103, Williamsburg, VA 23185; e-mail pchiro@performancechiropractic.com; visit us on FaceBook at http://www.facebook.com/performancechiro; or go to www.performancechiropractic.com