A pulling sled works by forcing your body to generate horizontal force against friction. You attach yourself to a weighted sled via a harness and strap, lean forward, and drive your legs into the ground to drag the sled across a surface. The resistance comes almost entirely from friction between the sled’s base and the ground, which means the surface you train on, the weight you load, and the length of your strap all change how the exercise feels and what it demands from your muscles.
The Physics of Friction and Force
Two types of friction govern how a sled moves. Static friction is the resistance you have to overcome to get the sled moving from a dead stop. Kinetic friction is the (slightly lower) resistance that acts on the sled once it’s already sliding. This is why the hardest part of any sled pull is that first step: you need to produce enough force to break the sled free. Once it’s moving, maintaining motion requires less effort, though the sled constantly tries to decelerate.
Unlike a barbell squat or deadlift, where you’re fighting gravity in a vertical line, a sled pull is dominated by horizontal force. Research from Bond University found that the horizontal force ratio during a heavy sled pull was roughly 39% at the first stride, compared to just 0.2% during a back squat. That makes sled pulls one of the most effective tools for training the kind of forward-driving force used in sprinting, tackling, and pushing off a starting line. As you stand more upright after the first few steps, your trunk angle changes and the horizontal force ratio drops to around 22%, shifting more effort into the vertical plane.
How the Strap and Harness Change the Load
The connection between you and the sled matters more than most people realize. A longer chain or strap creates a shallower angle of pull relative to the ground, which keeps more of your force directed horizontally. A shorter strap pulls at a steeper angle, meaning more of your effort goes into lifting the sled slightly rather than dragging it forward. Coaches who program sled work pay attention to strap length, harness position (waist versus shoulders), and even the type of attachment because each variable shifts the force demands on your body.
When you pull from a waist harness, your hips become the anchor point. Your legs drive backward into the ground, your hips extend, and the force transfers through the harness to the strap and then to the sled. A shoulder harness shifts the attachment point higher, which changes your trunk angle and can increase the demand on your upper back and core to stay rigid.
Which Muscles Do the Work
Sled pulling is a full lower-body exercise, but it doesn’t load every muscle equally. A study published in the Journal of Strength and Conditioning Research compared muscle activation during sled work to the back squat and found that the two exercises produced similar activity in the quadriceps, hamstrings, and deep core stabilizers. The biggest difference was in the calves: sled work produced 61% greater calf muscle activation than squats. That makes sense because each stride on a sled pull ends with a forceful push-off through the foot, demanding constant work from the lower leg.
The direction you face changes everything. Pulling forward (walking away from the sled) emphasizes the hamstrings, glutes, and calves as you drive into hip extension. Walking backward while dragging the sled flips the demand onto the quadriceps, since your knees are extending to push your body away from the sled with each step. This backward variation is especially popular for knee rehabilitation and joint health.
Why Sled Pulling Is Easy on Joints
Most loaded exercises have an eccentric phase, where your muscles lengthen under tension. Think of the lowering portion of a squat or the descent of a deadlift. That eccentric loading is what causes most muscle soreness and puts the greatest stress on joints. Sled pulling is almost entirely concentric: your muscles only shorten to produce force. The sled never loads you on the way back down because there is no “way back down.” You move the sled. The sled never moves you.
This distinction is particularly relevant for knees. During a squat, your body weight plus the barbell compress your knee joint as you lower and rise. During a backward sled pull, the resistance travels through a rope or strap behind you, and your knees push your hips backward rather than absorbing downward force. The result is significant quadriceps work with minimal joint compression. That’s why backward sled drags have become a go-to exercise for people rebuilding knee strength after injury or surgery, and for older athletes looking to train their legs without accumulating joint stress.
How Surface Changes Resistance
The ground you pull on is effectively a second variable you’re loading. A smooth concrete floor or indoor turf creates relatively low friction, so the sled glides and you can move faster or load heavier. Outdoor grass, rubber gym flooring, and asphalt all create different levels of drag. Outdoor grass is notably different from indoor turf, even though they look similar. The softness of natural ground, moisture, and uneven terrain all increase resistance in ways that are hard to predict or replicate indoors.
This means you can’t simply follow a weight prescription from one facility and expect it to feel the same at another. A 90-pound sled on polished concrete might feel equivalent to a 45-pound sled on wet grass. If you’re training for a specific competition like Hyrox, where sled pushes happen on indoor turf, practicing on that exact surface matters for dialing in your pacing.
Loading for Speed Versus Strength
How much weight you put on the sled determines what physical quality you’re training. Lighter loads moved quickly develop speed and acceleration. A study in the Journal of Human Kinetics found that young sprinters towing 10 to 20% of their body mass improved their rate of force development during sprint starts, making light sled towing a useful tool for early-phase acceleration. Heavier loads slow you down and increase ground contact time with each step, shifting the exercise toward pure strength development.
Many coaches program sled work on a continuum. On the light end (10 to 20% of body mass), the goal is fast, powerful strides that mimic sprinting mechanics. On the heavy end (50% of body mass or more), the goal is grinding, strength-dominant effort where each step is a battle against friction. Moderate loads fall somewhere in between, building what’s often called “speed-strength,” the ability to produce high force at moderate velocities. Your training goal determines where on that continuum you should work, and most athletes benefit from rotating through different loads across a training cycle.