Here's the thing nobody tells you about SI joint pain: it's maddeningly vague. You can't quite pinpoint it. It's somewhere in your lower back, maybe your buttock, maybe both. It feels different depending on the day. And because it doesn't scream at you the way a torn muscle does, you ride through it for weeks — sometimes months — before you take it seriously.
I did this myself. Rode through it for an entire spring, convinced it was just general lower back tightness from too much desk time. Turns out the problem was far more specific, and once I understood what was actually going on at the joint, fixing it was surprisingly straightforward.
Let me break this down.
What the SI Joint Actually Is
The sacroiliac joint sits where the sacrum (the triangular bone at the base of your spine) meets the ilium (the large wing-shaped bone of the pelvis). You have two of them, one on each side.
Unlike your hip or knee, the SI joint isn't designed for large ranges of motion. It moves only 2-4 degrees — just enough to absorb and transfer force between your upper body and your legs. Think of it as a shock absorber with almost no travel. It's held together by some of the strongest ligaments in the body, and when everything is working properly, you never think about it.
The problem is that "almost no movement" doesn't mean "no movement at all." The joint does move, and it can become irritated when load is applied unevenly or repeatedly in one direction. Which is precisely what cycling does.
How Cycling Loads the SI Joint
Here's where it gets really interesting from a biomechanical standpoint.
When you ride, your pelvis is fixed on the saddle. It doesn't rotate freely the way it does when you walk or run. Your sit bones are planted, and from that fixed base, your legs are driving alternating forces downward through the pedals — roughly 200-400 Newtons per stroke at moderate intensity, thousands of times per hour.
This creates three specific loading patterns that the SI joint doesn't particularly enjoy:
Repetitive asymmetric shear. Every pedal stroke pushes one side of the pelvis down while the other side remains relatively stable. Over a four-hour ride at 85rpm, that's roughly 20,000 asymmetric loading cycles per side. The ligaments around the SI joint are built to handle this, but only if the forces are reasonably balanced between left and right.
Fixed pelvic position. Walking and running allow the pelvis to rotate, tilt, and shift with each stride — distributing load across a wider area. On the bike, the saddle constrains this movement. The SI joint absorbs forces it would normally share with other structures.
Sustained flexion. The cycling position places the lumbar spine in flexion, which shifts the load-bearing pattern at the SI joint. Research by Burnett and colleagues has shown that sustained lumbar flexion during cycling increases posterior shear forces at the SI joint — exactly the type of loading most likely to irritate it.
None of this means cycling is bad for your SI joint. It means cycling loads it in a specific way, and if something in your setup or movement pattern is adding extra asymmetry to that load, the joint lets you know about it.
What SI Joint Pain Feels Like
The classic presentation is a dull ache on one side of the lower back, right around the belt line or just below it. It tends to sit just to one side of the midline — if you put your thumb on one of the two dimples at the base of your spine and press in, you're roughly over the SI joint.
A few patterns that suggest SI joint involvement rather than general lower back pain:
- One-sided. SI joint pain is almost always unilateral, at least initially. Dead-centre lower back pain is more likely lumbar in origin.
- Builds during long rides. Short rides might feel fine. The pain tends to accumulate with duration.
- Stiffness getting off the bike. That feeling of walking like you've aged thirty years in the first few minutes after dismounting. It loosens up after 10-15 minutes of walking.
- May shift sides. Some riders report that the pain alternates between left and right over weeks or months. This can happen as your body compensates — favouring one side, then overloading the other.
- Aggravated by single-leg standing. Standing on one leg to put your shoes on and feeling a catch or ache in the lower back/buttock area is a common report.
What it usually doesn't feel like: sharp radiating pain down the leg past the knee (that's more likely a disc or nerve issue), dead-centre spinal pain (more likely lumbar facet), or pain that's worse sitting than riding (possibly piriformis).
Self-Assessment: A Starting Point
A few simple tests can help you figure out whether the SI joint is likely involved. These are screening tools, not diagnostic — a physiotherapist doing a proper clinical assessment is always the gold standard. But they're useful for getting a sense of what you're dealing with.
The FABER Test
Lie on your back. Place the ankle of the affected side on the opposite knee, so your leg forms a figure-four shape. Let the bent knee drop outward toward the floor. If this reproduces your familiar pain in the lower back or buttock on the same side, the SI joint is a likely contributor.
Compression Test
Lie on your side with the affected side up. Have someone press down firmly on the top of your pelvis (the iliac crest), compressing the SI joints together. Pain on the affected side is a positive result.
Distraction Test
Lie on your back. Have someone press outward on both sides of your pelvis simultaneously, at the front of the iliac crests. This separates the SI joints. Again, reproduction of your familiar pain is what you're looking for.
The important caveat: no single test is definitive. Research by Laslett and colleagues showed that a cluster of three or more positive provocation tests gives the best diagnostic accuracy for SI joint dysfunction. One positive test is suggestive. Three positive tests from a trained clinician is much more reliable.
If you're getting positive results on these self-tests, the next step is addressing the most common cycling-specific causes.
Asymmetric Pedalling: The Hidden Driver
This is the one most riders miss. And it's the one that matters most.
Your left and right legs are almost certainly not producing identical force, at identical angles, through identical ranges of motion. Everyone has some degree of asymmetry. The question is whether that asymmetry is large enough to create meaningful uneven loading at the SI joint over thousands of repetitions.
Three common sources:
Leg Length Discrepancy
A genuine anatomical leg length difference of as little as 5mm can create significant asymmetric loading over a long ride. The shorter leg effectively pushes the pelvis into a slight lateral tilt on every stroke, creating shear at the SI joint.
Here's what most people do: nothing, because they don't know they have one. What actually works: get measured. A physiotherapist can assess true versus functional leg length difference (functional differences come from muscle tightness or pelvic alignment rather than actual bone length). True anatomical differences can be addressed with cleat shimming — adding a shim between the shoe sole and the cleat on the shorter leg.
Cleat Position Errors
If one cleat is even 2-3mm further forward, further back, or more rotated than the other, the resulting asymmetry in knee tracking and force application feeds directly up through the pelvis. This is one of the first things a good bike fitter checks.
Habitual Favouring
Power meter data consistently shows that most riders produce 48-52% of their power on their dominant leg and 52-48% on the other. This is normal and generally not a problem. But some riders run 55/45 or worse — often without realising — and that sustained imbalance is a direct ticket to asymmetric SI joint loading.
Single-leg drills on the turbo trainer aren't just for pedalling efficiency. They're particularly useful for identifying and correcting significant side-to-side imbalances.
The Stabilisation Programme
The most effective conservative treatment for SI joint dysfunction is strengthening the muscles that control pelvic stability. The logic is simple: if the muscles around the joint are strong enough to control its position under load, the ligaments don't get irritated.
Two to three sessions per week, 20-25 minutes each. Expect to see meaningful improvement within 4-6 weeks, with continued progress through 8-12 weeks.
Bird-Dogs
Start on all fours, hands under shoulders, knees under hips. Extend the right arm forward and the left leg back simultaneously, keeping the hips level — a stick balanced across your lower back shouldn't roll off. Hold for 3-5 seconds, return, and switch sides. This is Stuart McGill's go-to exercise for spinal stability, and for good reason — it trains anti-rotation and anti-extension simultaneously.
3 sets of 10 per side.
Dead Bugs
Lie on your back with arms pointing at the ceiling and knees bent at 90 degrees (shins parallel to the floor). Lower the right arm overhead and the left leg toward the floor simultaneously, keeping your lower back pressed into the ground. The moment your back arches, you've gone too far. Return and switch sides.
3 sets of 10 per side. Progress by straightening the lowering leg.
Side Planks
Lie on your side, propped on your forearm with elbow directly under the shoulder. Lift your hips so your body forms a straight line. Hold. This targets the quadratus lumborum and obliques — both critical for lateral pelvic stability.
3 sets of 30-45 seconds per side. Progress by lifting the top leg.
Clamshells
Lie on your side with knees bent at 45 degrees, feet together. Open the top knee like a clamshell while keeping the feet touching. You should feel this in the gluteus medius — the muscle on the outside of the hip that controls pelvic stability during single-leg phases.
3 sets of 15 per side. Add a resistance band around the knees to progress.
Glute Bridges
Lie on your back, knees bent, feet flat on the floor hip-width apart. Drive through the heels to lift the hips until your body forms a straight line from shoulders to knees. Squeeze the glutes at the top. Lower slowly.
3 sets of 15. Progress to single-leg glute bridges (same movement, one foot lifted off the floor) once you can do 15 bilateral reps with good form.
Banded Lateral Walks
Place a resistance band around the ankles (or just above the knees for a slightly different emphasis). Stand in a quarter-bend position. Step sideways, maintaining tension on the band throughout — don't let the trailing leg snap back.
3 sets of 15 steps each direction.
A note on what not to do: avoid heavy loaded exercises that compress the SI joint, particularly during the acute phase. The goal is to build stability and endurance in the pelvic stabilisers, not to pile maximum force through the joint.
Bike Fit Adjustments
Exercise alone won't fix SI joint pain if your bike is actively creating the problem. These are the fit variables most relevant to SI joint loading:
Saddle Tilt
This is the one that catches people out. A nose-down saddle angle causes your pelvis to slide forward continuously, so you're constantly bracing against the pedals and bars to stay in position. That bracing increases posterior pelvic tilt and compresses the SI joint.
A level saddle — verified with a spirit level, not eyeballed — is the starting point. Some riders with SI joint issues benefit from a very slight nose-up angle (1-2 degrees), which lets the sit bones bear weight more evenly. But start level and adjust from there.
Saddle Height
Too high, and the pelvis rocks side to side at the bottom of each pedal stroke. That lateral rocking is asymmetric loading at the SI joint, thousands of times per hour. If you see your hips swaying when you watch video from behind, your saddle is almost certainly too high.
Drop by 2-3mm and reassess after a week. The bike fit guide covers the full diagnostic process.
Cleat Shimming for Leg Length Discrepancy
If you've been assessed and have a confirmed anatomical leg length difference, cleat shims are the first intervention. These are thin wedges placed between the shoe sole and the cleat on the shorter leg. Start with half the measured difference — a 6mm anatomical difference typically starts with a 3mm shim — and reassess over 2-3 weeks.
Full correction in one step can create its own problems. The body has adapted to the asymmetry, and it needs time to readjust.
Crank Length
Shorter cranks reduce the range of motion at the hip, which can reduce the stress transmitted through the pelvis at the top and bottom of the pedal stroke. Riders with persistent SI joint issues who haven't responded to other fit changes should consider trying 165mm cranks — Phil Burt, former head of physiotherapy at British Cycling, has advocated strongly for shorter cranks in riders with pelvic and lower back issues.
When It's Not Actually Your SI Joint
Here's the thing — lower back and buttock pain in cyclists can come from several different structures that all live in the same neighbourhood. Getting the diagnosis wrong means the treatment won't work.
Hip labral tears can refer pain into the groin and buttock and are often aggravated by cycling's repetitive hip flexion. The distinguishing feature is typically a catching or clicking sensation in the hip, especially during deep flexion.
Piriformis syndrome presents as buttock pain and can mimic SI joint dysfunction closely. The piriformis muscle sits directly over the sciatic nerve in some people, and tightness or spasm can create pain that radiates into the buttock and down the back of the thigh. Sitting for long periods (including on a bike saddle) often aggravates it.
Lumbar facet joint irritation causes pain that's usually more central and worsens with extension (arching the back) rather than flexion. It can refer into the buttock and mimic SI joint pain.
Lumbar disc referral typically follows a more defined pattern — pain radiating below the knee, numbness or tingling in the foot, and pain that worsens with forward flexion and sitting. This is the one that needs prompt professional assessment.
If your symptoms don't match the SI joint pattern described above, or if they include radiation below the knee, numbness, tingling, or progressive weakness, see a physiotherapist before you start doing stabilisation exercises. Getting the right diagnosis first saves you weeks of treating the wrong thing.
Red Flags: When to See a Professional
Get assessed if any of the following apply:
- Pain radiating below the knee
- Numbness or tingling in the leg or foot
- Progressive worsening despite 6-8 weeks of targeted exercise and fit adjustment
- Pain that wakes you at night
- Bowel or bladder changes (this is rare but requires immediate medical attention)
- History of inflammatory conditions (ankylosing spondylitis has a predilection for the SI joints)
- Pain that started after a specific incident — a crash, a heavy fall, or a sudden sharp onset during a ride
The right professional for SI joint assessment is a sports physiotherapist or sports medicine physician. Ideally one who works with cyclists, because they'll understand the specific loading patterns and can assess both you and your bike.
Return to Riding Protocol
Once the acute pain has settled — meaning you can walk, sit, and perform daily activities without significant discomfort — you can start reintroducing riding. But the approach matters.
Weeks 1-2: Short, flat rides only. Thirty to forty-five minutes at zone 1-2. Stay seated. The goal is to test the joint under controlled conditions and see how it responds. If pain is present during the ride, stop.
Weeks 3-4: Gradually increase duration by 15-20% per week. Still predominantly flat, still predominantly seated. You can introduce moderate intensity (zone 3) for short intervals if pain-free.
Weeks 5-6: Begin reintroducing gentle rolling terrain. Keep standing efforts brief — 30-60 seconds at a time. Standing climbing loads the SI joint differently (more compression, less shear) and should be brought back gradually.
Weeks 7-8: Progress toward pre-injury volume and intensity. If pain returns at any point, drop volume by 30% and give it another week before trying to progress again.
Throughout this process, continue the stabilisation exercises. They're not just rehabilitation — they're maintenance. Two sessions per week as an ongoing commitment will keep the SI joint stable under load.
The Bigger Picture
SI joint dysfunction is one of those issues that sounds complicated but is usually straightforward to resolve. The science has finally caught up with what good physiotherapists have been saying for years: most SI joint pain in cyclists comes from a combination of asymmetric loading and insufficient pelvic stability. Fix both, and the joint settles down.
The mistake is treating it as generic lower back pain. A foam roller and some vague stretching won't cut it. Specific stabilisation exercises, targeted at the muscles that actually control the SI joint, combined with a bike fit that minimises asymmetric loading — that's what works.
If you're dealing with a niggle that matches what I've described, start with the stabilisation programme and check your saddle tilt. Those two changes alone resolve the majority of cycling-related SI joint issues.
Got questions about SI joint pain, bike fit, or any aspect of training and recovery for masters cyclists? The Roadman Cycling community on Skool is where the conversation continues — real riders working through real problems, no fluff.