What causes the ultramarathon “side lean” and what can be done to prevent and/or correct it? – Beth M.

Lateral trunk lean—when a runner leans to one side while running—is often observed during ultramarathons. It tends to manifest in the latter stages of a long race and, if you’re prone to side lean, it probably appears consistently on one side. Although it's tempting to impulsively attribute lateral trunk lean to a weakness in core stability—which we would correct with core exercises—the actual cause is more complex. It’s possible that a side lean would be initiated to offload an injured knee (1). However, assuming you’re not injured, the lean is more likely due to the muscles of the pelvis or legs being weaker on one side of the body, a strength imbalance that predisposes to fatigue. Trunk lean is not just a problem but a symptom.

Let’s take a step back for a moment (pun intended) because scientists are quite particular about the term “fatigue,” and it should be defined. In the context of running, fatigue generally denotes a decrease in a muscle’s contractile function which affects power output (and therefore pace). Fatigue has a central component (decreased neural activation of muscles by the central nervous system) and a peripheral one (due to local factors within the muscles, such as glycogen depletion) (2, 3). As one might expect, the extreme duration of most ultrarunning races makes fatigue very common. As mentioned above, fatigue may occur earlier on one side of the body than the other. This is because, despite the body’s obvious visual symmetry, it is common for athletes to exhibit left/right imbalances in muscle size and strength (4). In people with cerebral palsy, for example, lateral trunk lean is known as a Trendelenburg gait, and derives from a defective hip abductor mechanism. In this condition, weakness in the hip abductors—the gluteus medius and gluteus minimus—causes drooping of the pelvis to the opposite side (5). It’s likely that a similar mechanism predisposes ultrarunners to a sideways lean to offload the fatigued hip abductors. Weak hip muscles may also increase the risk of running-related injury—athletes with strength imbalances in the hip extensors tend to exhibit greater prevalence of lower-limb injury and/or lower-back pain (6).

Once muscle fatigue develops, there’s very little (other than rest) that can be done to attenuate it. Prevention is therefore the best strategy. Various non-evidence-based interventions have been proposed to help prevent, or at least mitigate, a sideways lean, including potassium supplements, Kinesio Tape and stretching. But these are short-term, quick-fix strategies that don’t address the underlying causes, analogous to papering over the cracks. Addressing the problem at its root cause means first performing some basic movement tests (perhaps aided by a physiotherapist or qualified strength and conditioning coach) to identify the pelvic or lower limb muscles in need of strengthening. Thereafter, resistance exercises to correct the strength or activation deficits should be incorporated into the training program.

I’m training for a mountain ultra (Bighorn in Wyoming) and will do most of my long runs on the trails. However, I have also tried treadmill running at a 6% decline and reverse walking at a 40% incline. Will the treadmill training help me prepare for the downhill component? – Eric N.

Some of my running friends have been talking about backward walking/running (retro running). Are there any benefits for endurance athletes? –@AlphaTan

Both of the questions above can be answered in the following. Downhill running requires the quadriceps (thigh muscles) and gastrocnemius (calf muscle) to resist your body weight against the force of gravity, effectively applying a “breaking force” to stop you from falling. This stress is unique to downhill running and causes more structural and functional damage to the muscle fibers when compared to level or uphill running. Fortunately, there is good scientific evidence that prior exposure to downhill running (i.e., becoming accustomed to it) will limit the magnitude of muscle damage, inflammation and soreness (7).

Walking/running backward—so-called “retro running”—simply activates the lower limb muscles in a different recruitment pattern to regular running. As a form of light exercise, backward walking has been practiced in China since ancient times. The idea that it must be beneficial on this basis is an appeal to antiquity—an informal fallacy that, in the same vein as the paleo diet and barefoot running, claims relevance partly because it correlates with tradition. But having ancient roots does nothing to legitimize a practice, and your decision whether to integrate it into your training regimen should be based on the intervention’s merit.

Proponents of retro walking say it challenges the body in ways that regular (forward) walking does not. They believe retro walking improves knee pain associated with arthritis and other joint abnormalities (specifically that it improves knee range of motion, quadriceps function, hamstring flexibility and gait and mobility), that it improves memory and that it evokes 10-fold greater energy expenditure than walking forward. But a key word search for scientific literature reveals very few studies on retro walking before 2011, and only a handful since. All of them have assessed potential benefits in patients with knee pain and/or osteoarthritis (8–11). A generous interpretation of these studies would be that incorporating backward walking into a physiotherapy-led program, alongside conventional treatment, may confer some benefits for people with pre-existing knee issues, but there’s certainly no data showing benefits for runners.

The idea that retro walking improves memory appears to stem from a series of experiments published in 2019 in which researchers studied the link between motion and temporal thinking. They found that walking backward after an audiovisual memory task improved recall of certain details; however, the same effects were apparent when subjects watched a video in reverse, and when they imagined walking backward (12). The positive effects on memory therefore have less to do with backward walking and more to do with how humans store and recall memories based on “temporal indexing.” That’s not the same as “backward walking improves memory,” as was reported in some mainstream outlets. Lastly, the claim that retro walking burns more calories than regular walking has not been studied. Because backward walking is considerably less efficient than forward walking, it’s feasible that it might also be more challenging from a metabolic and/or cardiovascular perspective. But as far as I can tell, the specific claim that retro walking evokes a “10-fold greater energy expenditure than forward walking” is folklore, attributed to an unidentified Chinese monk who once said, “A hundred steps backward is worth a thousand steps forward.” In summary, walking backward, on an incline or decline, won’t help you prepare for downhill running.

The most effective way to become accustomed to the stress is to get out on the trails and practice downhill sections. However, depending on where you live and the local climate, it may not be the most pragmatic. Running on a treadmill that has a decline function is a good alternative. Failing that, try integrating some eccentric muscle strengthening exercises (where the muscle is lengthening under load) into your resistance workouts. A cautious combination of all three strategies may be productive, and a “little but often” approach seems to yield the best results (13).

References

1.         Simic M, Hunt MA, Bennell KL, Hinman RS, Wrigley TV. Trunk lean gait modification and knee joint load in people with medial knee osteoarthritis: the effect of varying trunk lean angles. Arthritis Care Res (Hoboken). 2012;64(10):1545–53.

2.         Millet GY, Tomazin K, Verges S, et al. Neuromuscular consequences of an extreme mountain ultra-marathon. PLoS One. 2011;6(2):e17059.

3.         Martin V, Kerhervé H, Messonnier LA, et al. Central and peripheral contributions to neuromuscular fatigue induced by a 24-h treadmill run. J Appl Physiol (1985). 2010;108(5):1224–33.

4.         Franettovich M, Hides J, Mendis MD, Littleworth H. Muscle imbalance among elite athletes. British Journal of Sports Medicine. 2011;45(4):348–9.

5.         Krautwurst BK, Wolf SI, Heitzmann DWW, Gantz S, Braatz F, Dreher T. The influence of hip abductor weakness on frontal plane motion of the trunk and pelvis in patients with cerebral palsy. Res Dev Disabil. 2013;34(4):1198–203.

6.         Nadler SF, Malanga GA, DePrince M, Stitik TP, Feinberg JH. The relationship between lower extremity injury, low back pain, and hip muscle strength in male and female collegiate athletes. Clin J Sport Med. 2000;10(2):89–97.

7.         Bontemps B, Vercruyssen F, Gruet M, Louis J. Downhill Running: What Are The Effects and How Can We Adapt? A Narrative Review. Sports Med. 2020;50(12):2083–110.

8.         Alghadir AH, Anwer S, Sarkar B, Paul AK, Anwar D. Effect of 6-week retro or forward walking program on pain, functional disability, quadriceps muscle strength, and performance in individuals with knee osteoarthritis: a randomized controlled trial (retro-walking trial). BMC Musculoskelet Disord. 2019;20(1):159.

9.         Goonasegaran AR, Suhaimi A, Mokhtar AH. A randomized control trial on retro-walking improves symptoms, pain, and function in primary knee osteoarthritis. J Sports Med Phys Fitness. 2022;62(2):229–37.

10.       Gondhalekar GA, Deo MV. Retrowalking as an adjunct to conventional treatment versus conventional treatment alone on pain and disability in patients with acute exacerbation of chronic knee osteoarthritis: a randomized clinical trial. N Am J Med Sci. 2013;5(2):108–12.

11.       Grobbelaar R, Venter R, Welman KE. Backward compared to forward over ground gait retraining have additional benefits for gait in individuals with mild to moderate Parkinson’s disease: A randomized controlled trial. Gait Posture. 2017;58:294–9.

12.       Aksentijevic A, Brandt KR, Tsakanikos E, Thorpe MJA. It takes me back: The mnemonic time-travel effect. Cognition. 2019;182:242–50.

13.       Yoshida R, Sato S, Kasahara K, et al. Greater effects by performing a small number of eccentric contractions daily than a larger number of them once a week. Scand J Med Sci Sports. 2022;32(11):1602–14.