## The Case for Picking Up The Pace

Feb 21, 2017

Back when I was still in college, the campus employee wellness department put together an exercise incentive program called Walk to Rio, in the spirit of the upcoming Rio summer Olympics. The idea was if everyone who signed up performed enough collective exercise that equated to enough steps to cover the distance from Harrisburg, Pennsylvania to Rio de Janeiro (about 4,871 miles= about 11 million steps), the group would be eligible for various prize drawings. The program was mainly pitched as a walking initiative, and that is what a good portion of the people opted to do. When I first heard that this initiative was going to take place, I immediately recalled a gripe one of my professors had with people who walk for fitness, most people miss a key part of what that means.

There is a difference between normal, every-day walk, and walking for fitness or weight loss. Think about your own normal walking pace, does that pace really get your heart rate up? Now there are some who might answer that question, “Yes, if I walk for long enough.” and that’s fine this post is not meant to put those people on the spot. But for those who answer no to that question, then my next question would be, how long do they expect to obtain fitness improvements from walking? Because while starting with normal walking may be perfectly fine depending on the person, eventually there will need to be a progression to obtain one’s individual fitness goals, especially if that goal entails weight loss. The intensity must be taken into account. Higher intensity equals more calories burned during exercise, and unfortunately that is rather hard to accomplish with one’s normal walking pace.

The most basic principle of weight loss is the number of calories expended, must be greater than the number of calories consumed over a longer period of time. So let’s take a look at how many calories are burned by “normal” walking. For this purpose, I’m going to assume a leisurely walking speed of 3 mph and a 3.5% grade to account for some small hills on the walking route. Using the ACSM’s MET (metabolic equivalent) equation, I can figure out what level of aerobic capacity is needed to perform the activity (VO_{2} in ml/kg/min.) and from that, total estimated caloric expenditure. The ACSM’s equation is set up as follows:

(Speed (m/min.) x 0.1) + (%Grade x Speed (m/min) x 1.8) + 3.5 ml/kg/min

So first thing first, 3 mph needs to be converted to meters per minute (1 mph=26.8 m/minà3.0 x 26.8= 80.4 m/min). The 0.1 and 1.8 are mathematical constants arrived by calculating the relative oxygen costs of horizontal, and vertical forces produced by the legs while walking. The 3.5 ml/kg/min corresponds to the average aerobic capacity sustained by most people at rest, so any level of activity above rest, will elevate the aerobic demand above 3.5 ml/kg/min. It is in essence the “zero” point. So by filling in the converted measure of speed, we arrive at…

(80.4 m/min x 0.1) + (0.035 x 80.4 m/min x 1.8) + 3.5 ml/kg/min= 16.61 ml/kg/min

So 16.61 ml/kg/min is the level of aerobic capacity necessary to maintain a walking speed of 3 mph on this particular route. To obtain a caloric value from this, we use the next equation:

VO_{2 }(L/min) x 5 kcal/min x total mins. of activity

Note that we need to do two things to our aerobic capacity measure given to us by the first equation, one is to cancel out the weight of our walker, and the other is convert milliliters to liters (multiply by 1000) to arrive at a measure of liters per minute. So I’m going to assume our walker weighs 80 kg. (176.5 lbs.). Also, let’s say he/she walked for 30 minutes. That leaves us with a caloric expenditure of…

(16.61 ml/kg/min x 80 kg)/1000ml/L= 1.3284L/min

1.3284 L/min x 5 kcal/min x 30 mins= 199.26 kcal

So thus our person burns about 200 calories on this particular 30-minute walk. So what if we double that time to 60 minutes? We would expect this person to burn around 400 calories. Going back to our basic principle of weight loss, one might conclude if this person opted for hour-long walks instead of half-hour walks, over time this person would lose more weight. The answer to that question is, most likely yes, but the loss may not be as drastic as expected.

Unfortunately, when we look at the research, walking programs result in relatively minor improvements in body composition, and there is little significant advantage in increasing duration when measuring health parameters related to weight loss such as body mass, body fat percentage, and waist-hip ratio. Both these studies (and many others) did demonstrate that there are other measures of cardiovascular health that benefit more significantly from walking (i.e. VO_{2} max, blood pressure), but weight loss parameters again are not among those seeing a significant improvement through walking. Why is this the case?

The answer appears to be walking in this manner, does not stress the body’s cardiovascular systems enough to elicit much beyond modest weight loss. This goes back to my old professor’s complaint about the way people walk for weight loss. Most studies do not take into account walking intensity. The studies above, measured progress in terms of total step count, without really controlling for walking intensity. The reason for this is that with studies like these, researchers usually allow their subjects to self-select their intensity in an effort to improve the odds the subjects will exercise more consistently throughout the duration of the study. There are others however, like this one, that do take intensity into account, and have found that taking the effort to increase walking intensity over a strolling pace to a faster pace, does have some effect on the amount of weight lost over time. Thus, the solution for walking for weight loss, is to up the intensity. There are a pair of easy ways one can accomplish this with a walking program, proper fitness walking, or a walk-jog program.

Fitness walking pushes you beyond a typical moderate, or even a brisk walking pace. Fitness walking involves two key components: an increase in stride frequency, and adding in upper body motion. Stride frequency needs to increase in order to increase the amount of muscle contractions that occur over the duration of the activity in an effort to up the intensity. Now while the stride may need to be lengthened slightly to accommodate the increased stride frequency to avoid scuffing one’s feet on the ground, one must also be careful to not overextend the stride. This can put excessive strain on the knee joints with each foot strike, and increases the risk of ankle destabilization if there is some unevenness in the terrain. The movement of the upper body is achieved by an arm swing with the elbows bent and locked in at about a 90-degree angle. This serves a twofold purpose; firstly, by actively driving the arms, more calories are burned as opposed to a strolling pace walking when the arms move passively, and secondly, by moving the arms in sequence with the legs, it helps maintain balance. For a visual tutorial, here’s a quick video on fitness walking. This is the best option for those with significant musculoskeletal limitations or for people wanting to ease their way into the more intense second option, the walk-jog.

The walk-jog is simple enough in its own right; all that need be done, is to split up the time into intervals of jogging, and intervals of walking. This method burns more calories in a similar timeframe. So let’s go back to our original 80kg person this time on a walk-jog. This person still maintains a walking speed of 3 mph and is on the same route. But now he/she is going break those same 30 minutes down into blocks of two minutes of walking and 30 seconds of jogging at 4.5 mph. Because in exercise science and we have equations for everything, there is one to figure out intensity for a walk-jog program too.

First, we do our normal equation used above to figure out the VO_{2} values needed to sustain the activity at each of our two selected parameters (walking- 3 mph avg. 3.5% grade, jogging- 4.5 mph avg. 3.5% grade). The walking portion we already figured out requires 16.61 ml/kg/min to perform, so we only need to solve for the running portion.

(Speed (m/min.) x 0.2) + (%Grade x Speed (m/min) x 0.9) + 3.5 ml/kg/min

Note our two constants are different from the walking equation, because our legs distribute our forces differently when running. Once again we need meters per minute instead of miles per hour (4.5 mph x 26.8=120.6 m/min).

(120.6 m/min x 0.2) + (0.035 x 120.6 m/min x 0.9) + 3.5 ml/kg/min= 31.8 ml/kg/min

Next, we figure out the total amount of calories by taking our VO_{2} values and splitting them up by minutes spent doing the walking and running component of each interval throughout the duration of the activity (2 mins walking + 0.5 mins running= 2.5 mins per interval round. 30 mins total time/2.5 mins per interval round= 12 interval rounds). So we will accomplish 12 intervals of both walking and jogging within our 30-minute timeframe. And the final step is dividing by the total amount of time spent exercising.

(VO_{2 }walking x total interval time) + (VO_{2} running x total interval time) / total time

(16.61 ml/kg/min x (12 x 2 mins)) + (31.8 ml/kg/min x (12 x 0.5 mins)) / 30 mins= 19.624 ml/kg/min

Now we get to total calories, like we did before, by multiplying our ml/kg/min value by our person’s weight, converting to liters, multiplying by our conversion factor of 5kcal/min, then multiply by the total time spent exercising.

(19.624 ml/kg/min x 80kg)/1000 ml/L=1.5699L/min

1.5699 x 5kcal/min x 30 mins= 235.5 total calories

So just by doing bouts of light jogging every two minutes, we can burn an extra 35 calories. Doesn’t seem like much, but that is an extra 35 calories you wouldn’t have been burning otherwise. That is part of the reason walk jog programs may be a more attractive option for those looking to lose weight. And here’s another thing, if we run through the math once more, but double just the running duration part, not the total time, the total caloric expenditure comes to an estimated 260 calories. To achieve that number following our parameters for our walking only example, our person would have to walk for about another 10 minutes.

There is another element to versatility in the walk-jog is that those performing the exercise on a treadmill have two options for the jogging portion: increasing the speed is obviously one, but the incline can also be increased to arrive at a jogging pace, which may be preferable for some with musculoskeletal limitations that cap increases in stride frequency. Such conditions are most often seen in the elderly and the obese. Both exhibit lack of dynamic knee and hip flexion in their respective gaits, which causes a more rear-foot strike, and thus increases the ground reaction force that must be absorbed with each foot strike, which in turn leads to an increased risk of injury.

My final thought on this matter, and this is my personal favorite, the walk-jog has an added psychological benefit: the individual becomes more accustomed to higher intensity activity, which over time, could lead to the gradual adoption of more higher-intensity activities. So by slow-dosing individuals with small bits of higher intensity activities, this sets up a mental avenue for a person to become comfortable with the idea of doing more higher intensity exercise, furthering health benefits by potentially setting up a long-term health habit, one that burns more calories. This can even happen if one happens to chose fitness walking as a starting point, then eventually work up to a walk-jog.

With walking for weight loss, it’s clear that that step count is not the only factor that matters. I’d encourage anyone who is struggling with weight loss, and is on the fence about what to do about it, to give one of these two options a shot. Warmer weather is right around the corner, and no time like the present to start getting ready for it. Any further questions? Don’t be afraid to ask your trainer!