It’s odd to think of your spine as a bike frame that needs to be setup, but it is not far from the truth. A bit simplistic, but our spines are a complex frame of bones, nerves, muscles, tendons, and ligaments that function much like cables and pulleys. Spine stability and function is greatly dependent on the activation of the surrounding nerves and muscles above and below your lower back. By activation, we mean nerve activation; how well a muscle contracts (shortens) when it is called upon by a nerve impulse. Lower back stability is incredibly complex, akin to a giant musical orchestra. Back stability on a bicycle is highly dependent on how well your back muscles fire (or not).
Muscle Fatigue and Impaired Spinal Movement
Pedaling a gravel bike on non-paved roads ultimately requires more energy. More torque is required to turn the pedals and this force affects the back. Anything that increases our energy expenditure will cause nerve and muscle fatigue, leading to back pain. Many studies have looked at the effects of holding a static bent-forward (flexion) position on the all-important back muscles that help maintain correct posture and stability in the lower back. After prolonged periods of static flexion (when a cyclist is on the drops), these back muscles become less effective at generating the forces required to maintain spinal stability and posture.
In another study, scientists demonstrated that when cyclists pedaled to exhaustion, their hamstrings (rear thigh) and calf muscles became progressively more fatigued. Not surprising, this fatigue produces undesirable changes in nerve firing and muscle movement patterns, which then affects the back. More specifically, cyclists who were forward flexed in the lumbar region and also had their knees splayed out predicted fatigue and poor spinal posture and back pain.
The evidence above points to the fact that cyclists need to be strong in the lower back and core in order to avoid suffering the results of impaired movement patterns. This fact becomes even more apparent in gravel riding.
Addressing Your Posture
Pro riders spend many more hours in the saddle than us average Joes. Recreational cyclists spend most of their day slumped in an office chair and this can play havoc with your back. If you spend most of the day sitting (at a desk or in a car), optimize your set up so that you maintain a straight position, without slumping or rotation. A standing desk is a great option. Also, incorporate back stabilizing exercises into your daily routine.
Selecting Correct Frame Geometry
Though lower back pain more often arises as a result of fatigue and improper movement, there is no doubt that improper bike setup fatigues your back and leads to pain. Choosing a bike frame with the right geometry and getting a bike fit to ensure the correct riding position on the bike are both crucial to minimizing unwanted stress on your lower back, knees, shoulders and neck.
Gravel bikes are essentially a sub-set of road and mountain bikes. A gravel bike has different front-end geometry than a road bike. Basically, gravel bikes are said to have more trail. Trail in bike geometry terms is defined by fork rake (offset), head tube angle, and tire size. Increased trail is the reason gravel bikes are inherently more stable.
Long top tubes or stems can increase the chance of lower back pain by too much forward flexion. Also, a large drop from the saddle to the handlebar – often created by a short head tube or slamming the bars to the head tube, creating a low stack, will force your back into excess flexion.
Similar to a road bike, this should be positioned so that when the pedal is at the bottom of the stroke and the ball of your foot is on the pedal, your knee should have a slight bend. With the pedals adjusted so that they are at the three o’clock and nine o’clock positions, a vertical line dropped from just behind the kneecap on the outside of the forward knee should pass through the axle of the pedal. The hips shouldn’t move sideways during pedaling and you shouldn’t have to stretch at the bottom of the pedal stroke. You may want to aire on the side of more knee flexion at bottom dead center because gravel riding involves more sitting and standing movements due to the nature of off-road riding.
You should be able to comfortably reach the bars from an upright position and your elbows should be slightly bent when resting on them. You should not have to stretch to reach the bars. Since most gravel riding is done in the upright position, be sure this position is comfortable.
Tire Choice and Comfort
Gravel riding usually involves hours of relentless rattling from the gravel that can really wear you down and fatigue your back. Tire choice is one of the most talked about equipment choices for gravel riding and racing. Most get into the sport thinking that a 35 C tire is sufficient, but many successful gravel riders in the popular Dirty Kanza race use even bigger volume tires. Basically this allows one to put less air and allows the tire to soak up more of the bumps, decreasing the vibration forces to the spine.