by Jordan Smothermon and Rob Shaul
We work with both mountain and tactical athletes. Over the years as our programming has evolved and resulted in a hearty exchange of work, and lessons learned, between the two programs.
On the Tactical side, we’ve recently undertaken a “Ruck Deep Dive” project – to closely examine loading and training for loaded movement. “Rucking” is the military term for hiking under load. As you can imagine, this is a huge issue for the military as soldiers must wear body armor, carry weapons, ammo, water, communications equipment, and other gear as they conduct patrols and missions. Rucking performance and injury prevention are hugely important for military operations and personnel.
Movement over ground under load is also key for many mountain sports – from day hiking to backpacking, to big mountain alpinism, alpine climbing approaches and fast peak bagging efforts.
As part of our Ruck Deep Dive project, we’ve conducted a research review of work the military has already done on this subject. We discovered five “thumb rules” which are just as applicable to mountain sports as they are to combat operations.
Here are the 5 Thumb Rules:
1) One pound on your feet equals five pounds on your back. (1 lb. feet = 5 lb. back)
2) One pound on your feet equals five percent more energy expended. (lb. ft = 5% more energy)
3) Every one percent of your body weight makes you six seconds slower per mile. (1% BW = +6 sec./mi.)
4) Ten percent grade incline cuts your speed in half. (10% uphill = 1/2 speed)
5) Going up slows you down twice as much as going down speeds you up. Every percent of incline adds 15 seconds to your mile pace. Every percent of decline takes 8 sec. off of your mile pace. (Uphill = +15 sec./mi.; Downhill = -8 sec./mi.)
1. One pound on your feet equals five pounds on your back.
This old backpacking thumb rule holds true, according to a 1984 study by the U.S. Army Research Institute. They tested how much more energy was expended with different footwear (boots and shoes) and concluded that it takes 4.7 to 6.4 times as much energy to move at a given pace when weight is carried on the shoe versus on the torso. In practical terms, this means you could carry half a gallon more of water (a little over 4 pounds) if you buy boots that are a pound lighter, which isn’t hard to do; and that’s a lot of water. Now imagine the energy savings of backpacking in light trail running shoes rather than heavy, leather backpacking boots over the course of a 7-day backpacking trip.
2. One pound on your feet equals five percent more energy expended.
Heavier footwear doesn’t just affect you because of their weight. They’re stiffer and less responsive as well. This reduces the efficiency of your body’s stretch reflex on hitting the ground.
Five percent doesn’t sound like much, though, so how does five percent translate to run times? Well, five percent would slow your mile pace time down by 30 seconds, depending on how long you’re running. But, the faster you attempt to run, the more than five percent will affect your performance.
3. Every one percent of your body weight in your pack makes you six seconds slower per mile.
Carrying weight in your pack isn’t free of cost, though. Each 1% of your body weight carried in your pack 6 seconds slower per mile. So, if you weigh 150 pounds, every 1.5 pounds of weight in your pack slows you by 6 seconds/mile. For a 150 pound hiker, on an extended trip, cutting his pack weight down from 40 pounds to 30 pounds saves him 40 seconds per mile.
4. Ten percent grade incline cuts your speed in half.
Grade greatly affects speed. By “grade” we mean how much terrain incline or decline there is. Percent grade is a term that describes how much you go up versus how much you go forward. 10%, for example, means that for every 10 ft you travel forward, you’ll travel 1 ft. up. In terms of angles, 10% equals 5.74 degrees. A 5.74 degree angle doesn’t seem like much until you’re humping up it mile after mile. You’ll know how hard it is because you’ll move twice as slow over it than over flat ground with a given load.
That last little part – with a given load – is important. A 10% grade will cut your speed in half no matter if you’re carrying 45 lbs. or 80 lbs.
5. Going up slows you down twice as much as going down speeds you up.
Don’t believe you’ll make time up on the other side of the hill. You won’t. You’ll only make half the time up. Famous running coach Jack Daniels provides numbers to this relationship, saying that uphills will add 12-15 seconds to your mile time and take off 8 seconds from your mile time on downhills. Another run guru, John Kellogg, says that for every 10 ft. of elevation change (up or down) changes your run time by 1.74 seconds, which, of course, is confusing as hell stated as an English sentence. Maybe it’s easier to think of it like this: if your uphill is 100 ft. up hill, you’ll run it 18 seconds slower than you would over flat ground.
Why don’t you gain as much by running down hill as you lose running up? Braking forces. As you descend, you have to brake your speed with your quads to keep yourself under control. The steeper the downhill, the more braking. This added load on your muscles further affects your uphill performance if you have repeated bouts of up and down work.
Sources:
- The energy cost and heart-rate response of trained and untrained subjects walking and running in shoes and boots by Bruce H Jones, Michael M. Toner, William L. Daniels och Joseph J. Knapik. US Army Research Institute of Environmental Medicine, Natick, Massachusetts, USA. Publicerad i Ergonomics1984, vol. 27, No.8, 805-902.
- Energy cost of backpacking in heavy boots by S. J. Legg and A. Mahanty, Army Personnel Research Establishment, Farnborugh, Hants, England. Publicerad i Ergonomics, 1986. Vol. 29, No. 3.
- Paavolainen, L.; Nummela, A.; Rusko, H., Muscle power factors and VO2 max as determinants of horizontal and uphill running performance. Scandanavian Journal of Medicine & Science in Sports 2000, 10 (5), 286-291.
- Gottschall, J. S.; Kram, R., Ground reaction forces during downhill and uphill running. Journal of Biomechanics 2005, 38 (3), 445-452.
- http://www.letsrun.com/forum/flat_read.php?thread=197366&page=0
- The Modern Warrior’s Combat Load – Dismounted Operations in Afghanistan. U.S. Army Center for Army Lessons Learned. April – May 2003. pg. i-115.