Summary: Preloading refers to movements that stretch activate muscles before they contract.
Preloading is important because pre-activated muscles generate greater force than muscles that are simply contracted.
Learn how to identify the leg preload in skate and classic skiing, and ways to make your preload more effective.
If I asked you to jump up as high as you can, you’d probably do a countermovement jump, not a squat jump.
You start a countermovement jump from the standing position. Next you crouch down, then spring up into the air. In a squat jump, you start from the crouched position, then jump straight up.
The Countermovement Jump Wins Every Time
Even with an equal leg push, you’ll get more height from a countermovement jump than from a squat jump: athletes can typically jump 3-6 cm higher with a countermovement jump. Most people know this instinctively, even if they’ve never studied exercise or biology.
The reason you get more height with a countermovement jump is because of a feature of muscle physiology called the Stretch Shortening Cycle.
The Stretch Shortening Cycle: How it Works
Muscles can contract concentrically, which means they shorten as they’re activated. When you lift a dumbbell with a bicep curl, you’re concentrically contracting your biceps.
Muscles can also work eccentrically. In this case the muscle is lengthened, or stretched, as it is activated. Lowering a weight during a bicep curl is an example of an eccentric contraction (of the biceps).
The Stretch Shortening Cycle is a combination of these 2 types of muscle contraction. During the SSC a muscle is rapidly stretched (eccentric contraction), then immediately shortened (concentric contraction).
The thing that’s so interesting about the SSC is that a muscle that’s rapidly stretched before it’s shortened will generate much greater force than a muscle that simply contracts concentrically.
That’s why the countermovement jump can generate more height than a squat jump – as you drop into a crouch from the standing position, you stretch activate your leg muscles just before they contract during the jump.
The stretch activation of your muscles immediately prior to contraction is also called a muscle “preload”.
All Muscles Can Be Preloaded
Typically, when cross-country skiers talk about a “preload”, they’re talking about countermovements that pre-activate the leg muscles in both classic and skate techniques. But SSC is a characteristic of all muscles and all muscles can be preloaded.
For example, the triceps are often preloaded when your poles first contact the snow. If your pole tip contacts the snow with enough force, your arm will flex at the elbow, which stretches the triceps just prior to their contraction during the pole push. You can see this quite clearly in this slow motion video of the Canadian national team skier, Heidi Widmer, sprint double poling.
Preloading the Leg Muscles in Cross Country Skiing
We want to focus on preloading the leg muscles during the kick. (The kick is the leg push. In classic skiing you push down and back against the snow, in skate skiing you push out to the side. The kick is not about swinging your leg forward like you’re kicking a ball.)
You’ll hear cross-country skiers talk about the “preload” in both classic and skate skiing. They’re talking about the sharp, downward pushing action at the start of a leg push. It’s similar to what happens in a countermovement jump when you abruptly drop into a crouch position by flexing at the ankle and knee. If you look closely, you’ll notice that the leg always flexes, then straightens during the leg push. This is true in both skate and classic skiing.
Like I already said, preloading pre-activates the leg muscles so they generate more force. But in cross-country skiing, especially classic skiing, the preload is also important because it compresses the ski’s camber against the snow. (The camber is the ski’s flex. You can see it when you hold a pair of skis with their bases together.)
In two of the classic ski techniques, diagonal stride and kick double pole, the preload sets the wax pocket against the snow. That’s important because it gives you something to push against. If you can’t compress your camber and make your wax pocket stick to the snow, you’ll slip and feel frustrated.
Preloading confused me for a long time. So, in case you’re struggling like I did, here’s a recap:
- The preload is the first part of your leg push.
- You “drop” your weight to push against the snow during the preload. You want a lot of flexion at the ankle.
- The preload both pre-activates your leg muscles and sets your ski against the snow
I think everyone preloads their leg muscles, even shufflers, but not everyone has an effective preload. Here’s a few suggestions for improving yours. Improving your preload will increase the force generated by your leg push and help you ski faster.