Back pain in runners: navigating ups and downs

The impact of gradient

Downhill running is known to increase impact forces and eccentric muscle demands (where muscles lengthen on footstrike to absorb these impacts), potentially elevating spinal compressive and shear forces. If downhill running also increases lumbar lordosis, the combination of the two, combined with inadequate trunk muscle activation and/or strength (particularly strength of the abdominals and erector spinae) might predispose runners to lower back strain injuries⁽⁹⁾. That’s because these core muscles have to work synergistically to maintain spinal alignment, and their activation patterns vary with terrain In short, the trunk’s role in stabilizing the pelvis and absorbing forces is crucial, yet studies on how running up and downhill affects trunk kinematics, trunk muscle activity and how these might impact on the risk of low back pain in runners are scarce.

New research

For runners who are prone to episodes of back pain, fully understanding how gradients encountered during training affects trunk stability, lordosis and movement patterns is vital for designing training and rehabilitation programs to prevent or manage LBP. This is particularly relevant for runners who have to train or compete on varied terrains, and for coaches and physios seeking to develop training programs that reduce lower-back injury risk during running. The good news is that a new study has attempted to provide some answers by investigating how different gradients influence trunk and pelvic posture, and muscle activity⁽¹⁰⁾. Published in the ‘International Journal of Sports and Physical Therapy’, this study examined how running on six different uphill and downhill gradients affected back and pelvic posture, and also how these gradients impacted muscle activities in trunk and lower limb muscles.

What they did

To carry out this study, 12 healthy recreational runners (six men, six women, average age 26.8 years) were recruited. Following some familiarization trials to ensure the runners were comfortable performing graded running tasks on a treadmill, the participants performed a protocol consisting of number of experimental trials:

·        Downhill running for 30 seconds with a gradient of -15%

·        Downhill running for 30 seconds with a gradient of -10%

·        Downhill running for 30 seconds with a gradient of -5%

·        Level running for 30 seconds – ie a gradient of 0%

·        Uphill running for 30 seconds with a gradient of +5%

·        Uphill running for 30 seconds with a gradient of +10%

All trials were run at 10kmh (6.2mph) with a randomized order of trials to minimize any order effects. The protocol included a 5-minute warm-up at 0% gradient. Participants wore standardized running shoes to control for footwear effects, and all the trials were run in a single session in order to maintain consistency and eliminate session-to-session effects.

What they measured

To assess back and pelvic posture and to determine how gradient running alters trunk posture and muscle activation, the researchers measured trunk and pelvic movement patterns using a 10-camera 3D motion capture system, with reflective markers placed on various anatomical landmarks such as the iliac crest of the pelvis and L1-L3 of the lumbar vertebrae. The patterns measured during running included trunk lean angle (forward/backward relative to the pelvis) and pelvic tilt (anterior/posterior rotation – see figure 2). Surface electromyography (sEMG – a method of measuring electrical activity in muscles) recorded muscle activity in eight muscle groups on both the runners’ left and right sides, including the erector spinae of the lower back, rectus abdominis of the stomach, external oblique, gluteus maximus (buttocks), biceps femoris (hamstrings), rectus femoris and vastus lateralis (quads), and gastrocnemius medialis (calves). All of these measurements were chosen to capture key factors in spinal loading and injury risk. In addition, heart rates (via a Polar monitor) and rate of perceived exertion (using the Borg 6-20 scale) were also monitored to assess cardiovascular and perceptual demands.

Figure 2: Anterior and posterior rotation of the pelvis

Ideally, the pelvis neither in a anterior rotation nor a posterior rotation, but instead in neutral rotation. Note how anterior rotation increases lumbar lordosis. (Image courtesy of SequenceWiz.org).

What they found

There were a number of findings relating to movement patterns, muscle activity and gradient changes that could have implications for runners prone to back pain. These were as follows:

·        Downhill running - In terms of trunk posture changes, the runners exhibited a backward-leaning trunk position, which increased lumbar lordosis (see figure 3), which as we have seen is associated with greater torque and shear forces that may elevate injury risk if not managed properly.

·        Uphill running - Runners shifted to a forward-leaning trunk position, reducing lumbar lordosis. This change, along with decreased pelvic tilt at moderate uphill gradients (+5% and +10%), can lower spinal loading compared to downhill running, potentially reducing strain on the lower back.

·        Muscle activity of erector spinae – Showed reduced activity during downhill running, which may limit the muscle’s ability to stabilize the spine, potentially contributing to increased lumbar lordosis and strain.

·        Muscle activity of the abdominal and hip muscles - The rectus abdominal muscles played a role in counteracting buckling and distributing impact forces during both uphill and downhill running. Hip muscles (eg glutes and hamstrings) showed higher activation during downhill running, helping to support trunk stability. However, this also indicates greater eccentric demand, which could lead to fatigue, and affect spinal control during longer runs.

·        Physiological and perceptual demands – Despite lower cardiorespiratory demand (ie lower heart rates), the rate of perceived exertion (RPE) was elevated during downhill running due to high-impact forces on musculoskeletal tissues. This suggests that the mechanical stress from downhill running may contribute to muscle fatigue and reduced function, increasing vulnerability to lower back strain, especially in untrained runners. Meanwhile, during uphill running, both heart rate and RPE increased predictably, reflecting the higher metabolic demand. However, the forward-leaning posture and reduced lumbar lordosis offered a biomechanical advantage for spinal stability.

·        Lower-limb kinetics - Downhill running increased activity in the gastrocnemius muscle (at -15%) and vastus lateralis (across all downhill gradients), reflecting greater eccentric loading to dissipate energy. This can indirectly affect trunk stability, as lower limb muscles contribute to the kinetic chain, and fatigue here may compromise control. Uphill running promoted mid- to forefoot strike patterns, reducing loading rates compared to the rear-foot strikes common in downhill running. This shift may decrease impact forces transmitted to the spine.

Figure 3: Changes in lower back lordosis while running at varying gradients

Each green box shows one of the six gradient conditions. The horizontal bar in the box shows the average result for that condition. The vertical size of the box represents the range of results. During the downhill runs (-15%, -10% and -5%), lordosis was increased. On the level (0%), lordosis was neutral. During the uphill runs, lordosis was reduced.

Implications for runners

This research has several implications for runners who have suffered or are trying to recover from a lower back strain (or wish to avoid one in the future). The key finding for runners is that during downhill running, the backward-leaning posture and increased lumbar lordosis can heighten compressive and shear forces on the spine, which may worsen a lower back strain or delay recovery from back pain. Therefore, if you have are suffering or have previously suffered from back pain, you should approach downhill running cautiously, especially on steep gradients (-15%), where the erector spinae muscles may not sufficiently stabilize the spine. This is particularly true for longer sections of downhill or for downhill sections later on in a run, when the elevated perceived exertion and impact forces can lead to additional muscle fatigue, further reducing trunk stability.

By contrast, a forward leaning posture and reduced lumbar lordosis during uphill running may lower the risk of spinal strain, making it a safer option for athletes recovering from or with a history of lower back injury. Moreover, incorporating uphill running into a training program can improve strength endurance and neuromuscular coordination, which may protect against trunk instability. Of course, when running a circular route outdoors, what goes up must come down! If you can therefore, try to run a hilly route with the longer sections of downhill earlier during your run (when you’re fresh), saving the uphill sections for later in run (where the accumulated fatigue matters less). Another option, especially recommended for runners who are recovering from back injury, is to begin with uphill sessions on a treadmill (no downhill needed!) running a bit more slowly with a gradient of 5-10% set. When resuming running outdoors, start off with flat runs, and only introduce mild downhill sections (of no more than) 10% very gradually.

Last but not least, don’t forget the importance of building and maintaining core strength to enhance spinal stability. Exercises such as planks, glute bridges, and hip extensions can enhance core and posterior chain strength, reducing the risk of dynamic instability during running. Monitoring training load spikes is also critical, as sudden increases in either intensity or volume can exacerbate lower back pain risk, even if overall mileage on a month-to-month basis is unchanged. Finally, ensure you perform a proper pre-run warm-up; not warming up can increase lumbar spine loading due to poor activation of the muscles that protect the spine. Perform a dynamic, mobility-type warm-up (ie not using static stretches) a targeting the core stability and hip muscles, thereby preparing the trunk for the hills ahead!

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