Ground Reaction Forces in Golf
When to “Kick” Into the Lead Leg
The Timing of the Front-Leg Post for Power and Control
If you watch elite players in slow motion, you’ll see the same lower-body pattern over and over:
They shift pressure toward the target.
They break that lateral move by posting into the lead leg.
They press vertically into the ground and rotate through.
That moment when the front leg “posts” is not just style—it’s the hinge point where lateral motion turns into vertical force and rotation. Get the timing wrong and you’ll feel stuck, spinny, or out of control. Get it right and the club feels like it’s being launched past you.
In this post we’ll break down:
What the lead-leg post actually is
How lateral → vertical ground reaction forces (GRFs) are sequenced
What’s happening anatomically when you “kick” into the left leg
Practical feels and drills to train the timing
1. Ground Reaction Forces: Shift → Brake → Press
From a physics standpoint, the lower body is interacting with the ground in three main directions: lateral, rotational (torque), and vertical ground reaction forces.(Titleist)
A simplified sequence for an efficient downswing looks like this:
Shift (Lateral GRF)
Pressure moves from trail foot toward lead foot in early downswing.
This is often seen as the “bump” of the pelvis toward the target.
Brake (Lateral → Rotational)
The lead leg begins to resist further lateral motion—this is your post.
That braking action creates a pivot point for the pelvis to rotate around.
Press (Vertical GRF)
With pressure loaded into the lead side, the golfer drives down into the ground.
The ground “pushes back” (vertical GRF), helping extend the lead leg and rotate the pelvis faster.(Taylor & Francis Online)
Force-plate data on skilled players consistently shows:
A rapid rise in vertical GRF under the lead foot beginning in the mid-downswing, peaking before or around impact.(Gavin Publishers)
Higher braking forces in the lead leg compared with the trail leg—Tour players show ~40–60% stronger braking in the lead leg.(AMTI)
The key takeaway: you don’t just “jump” up. You first shift, then brake, then press.
2. What Is the Lead-Leg Post?
When we say “post into the front leg,” we’re talking about three things happening together:
Lateral braking – the pelvis stops sliding toward the target.
Hip & knee stabilization – the lead side stiffens enough to transmit force.
Rotational pivot – the pelvis begins to rotate around the now-stable lead hip.
On a pressure plate or force plate, this shows up as:
Center of pressure moving into the lead foot,
A spike in lead-side lateral braking force, followed by
A strong vertical force spike as you press into the ground.(Gavin Publishers)
On video, you’d see:
Lead hip bumping slightly toward target in transition,
Lead knee flexing a bit as pressure loads,
Then the lead leg straightening and pelvis opening aggressively through impact.
3. Anatomy of the “Kick” Into the Lead Leg
Now let’s zoom in on what your body is actually doing when you “kick” into that left leg (for a right-handed golfer).
a) At the Hip: Glutes and Rotators
Primary players:
Gluteus maximus – hip extension and external rotation
Gluteus medius/minimus – stabilize pelvis, control hip adduction/abduction
Deep external rotators (piriformis, etc.) – help rotate the femur in the socket
What’s happening:
During the shift
The lead hip moves into slight flexion and adduction as the pelvis shifts toward the target.
Glute med/min are working hard to keep the pelvis stable over the femur.
During the post (brake)
The lead glute max and lateral hip musculature fire eccentrically to slow the pelvis’ lateral glide.
This “braking” creates a firm pivot point.
During the vertical press
The glute max shifts from eccentric to concentric work, extending the hip and supporting the upward/rotational move.
This helps the lead side clear and opens the pelvis toward the target.
Recent biomechanical studies on hip and knee joint moments confirm that peak hip extension and abduction moments in the lead leg occur during the downswing and into impact—right when golfers are posting and rotating hardest.(PubMed Central)
b) At the Knee: Quads vs. Hamstrings
Primary players:
Quadriceps (especially vasti group) – knee extension
Hamstrings – help control tibial motion and assist with hip extension
What’s happening:
Flex to load
As you shift into the lead side, the lead knee typically flexes slightly.
This increases the ability of the quads to produce force—think of it as “cocking the spring.”
Extend to post
As you brake lateral motion and start pressing vertically, the quads extend the knee.
This extension is part of the classic “posting up” look.
Studies of lower-limb joint moments during the swing show significant knee extension moments in the downswing, aligning with the timing of vertical GRF peaks.(PubMed Central)
c) At the Ankle: Plantarflexors and Foot Pressure
Primary players:
Gastrocnemius and soleus – plantarflexion (pressing the foot down)
Intrinsic foot muscles – stabilize the arch and manage pressure shifts
What’s happening:
As pressure moves to the lead foot, plantarflexors help you push into the ground.
You’ll often feel more pressure under the lead heel and mid-foot, not just the toes.
That directed pressure into the ground is what allows the vertical GRF to “launch” you into rotation.
Network meta-analysis on GRFs and foot position shows that how and where you load the feet meaningfully changes your force profile and club speed potential.(MDPI)
4. When Should the Lead-Leg Post Happen?
Here’s the big timing question: when do you actually kick into that left leg?
In most efficient swings:
Lateral shift begins early in the downswing (roughly transition to lead-arm parallel).
Lead-leg braking and vertical GRF buildup ramp up between lead-arm parallel and shaft-parallel in the downswing.
Peak vertical GRF under the lead foot typically happens before impact, not after.(Gavin Publishers)
In other words:
You should be posting and pressing into the lead leg while the club is still working down, so the energy has time to travel up the chain to the torso, arms, and clubhead.
If you wait to “jump” until you’re at or past impact, you’ve missed the window—now you’re just standing up.
5. Practical Feels to Train the Sequence
Here are some performance-friendly feels we use with golfers at ATX Golf Performance to dial in the timing.
Feel 1: “Slide, Sink, then Push”
On a slow-motion downswing, feel the pelvis slide a few inches toward the target.
As it does, feel the lead knee soften and “sink” slightly—that’s your load.
Then feel yourself push the lead foot into the turf as your chest starts to rotate open.
Key idea: you’re not jumping at the ball. You’re pushing into the ground and letting the ground help you rotate through.
Feel 2: “Brake with the Hip, Not the Head”
From lead-arm parallel, imagine your lead hip “hitting the brakes” while your upper body keeps turning.
Your head and sternum stay relatively centered; the brake happens at the pelvis, not the chest.
This encourages the proper pivot instead of a full-body slide.
Feel 3: “Straighten Late”
A common amateur pattern is straightening the lead leg too early, which kills rotation and leads to early extension.(GOLFTEC)
Feel the lead knee stay flexed longer into the downswing.
Then, as the hands approach hip height, let the leg extend as you rotate hard.
The feel is: soft → loaded → straightening through impact, not rigid from the top.
6. Common Errors With the Lead-Leg Post
Error 1: Sliding Through Without Braking
Too much lateral motion, not enough braking.
Symptoms: fat/thin shots, blocks, weak high fades.
Fix: exaggerate the feeling of the lead hip “stopping” and the pelvis turning around that side.
Error 2: Early Vertical Push
Pushing up too soon (often from the trail foot)
Symptoms: early extension, loss of posture, heel strikes, inconsistent low point.
Fix: sequence your forces: shift first, then brake, then press. Don’t chase vertical force from the top.
Error 3: Locking the Lead Leg Too Early
Posting into a locked lead knee at the start of the downswing.
Symptoms: low-back stress, inconsistent contact, difficulty controlling face-to-path.
Fix: keep a small amount of flex as you shift, then straighten as you rotate through the ball, not before.
7. Bringing It Back to Your Game
Here’s the simple performance summary:
The lead-leg post isn’t just “standing up.” It’s a coordinated braking and vertical press that happens while the club is still in the downswing.
Anatomically, you’re using glutes, quads, calf, and foot musculature to first absorb and then generate force—eccentric load, then concentric drive.
From a force-plate perspective, you want a clean lateral shift, strong lead-leg brake, and well-timed vertical force spike that peaks before impact.
At ATX Golf Performance, we use technology like force plates and 3D motion capture to measure exactly how and when you’re using the ground—then we translate that data into feels and drills that make sense in your body.
If you feel like you’re:
Stuck on the back foot,
Spinning out of the shot, or
Standing up and losing compression,
a session focused specifically on lead-leg posting and GRF timing can change your ball flight fast while staying safe for your joints.