Busting the Myth: Runners Don't Need Strength Training
Running-related injuries are very common, with an incidence of up to 79.3% . The following are areas of the lower limb that are most commonly injured:
Knee (up to 50%)
Upper leg, lower leg and foot.
Ankle and hip/pelvis are less common.
Like most injuries, these occur because runners aren’t compliant with maintenance exercises to help their body recover properly and maintain strength. However, there are other factors that determine the risk of a lower-extremity injury:
Systemic factors (e.g. age, gender, height, and weight / BMI)
Running / training related factors (e.g. training frequency, training duration, training distance, warm ups, and running experience)
Health factors (e.g. medical history and history of previous injuries)
Lifestyle factors (e.g. smoking, alcohol intake, and other physical activity)
If we break running down, it is essentially repeated single leg falls and balances. With each step onto a single leg, the load can multiply by 3-4x your body weight, so it is important runners have enough lower-limb strength to account for this.
How does strength training benefit runners?
Running economy is a complex phenomenon that encompasses many patho-physiological characteristics during sub-maximal running. It is determined by the energy demand (volume of consumed oxygen, VO2) of the body at a particular running velocity - often termed “steady state.” Strength training increases lower-limb coordination and muscle co-activation, which improves running economy by increasing muscle stiffness and decreasing ground contact times.
To achieve the desired effect in highly trained distance runners, low to high intensity strength training should be completed 3-4 sets of 8-15reps, 2-3x / week for 8-12 weeks. Exercises may include skater squats, single leg squats, lateral step downs, hopping and jumping, arabesques and heel raises. An improved running economy means that runners run faster, something that we all want to be able to do! 
When focusing on strengthening exercises, it is important that they target multiple areas of the body. Recent research has shown that recreational runners who performed just a foot core strengthening protocol were up to 2.42 times less likely to experience a running-related injury at 4 to 8 months into the program! 
So why don’t runners do strengthening exercises?
1. There is a belief amongst many runners that increasing muscle mass and “bulking up” will impede performance by slowing them down. However, there is no evidence backing this so-called “interference effect.” 
2. The belief that stretching and foam rolling is all that is needed. It does play a vital role in recovery, but it should not be the only thing that runners do.
3. Runners generally have no awareness of the benefit of strength training. Strength training has been shown to have many benefits on long-distance running performance including improved running economy, rate of force development, maximal sprint speed and time trial performance. 
If you are a runner and want to increase your performance and reduce injury, then get strengthening!
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 Balsalobre-Fernández C, Santos-Concejero J, Grivas GV. Effects of Strength Training on Running Economy in Highly Trained Runners: A Systematic Review With Meta-Analysis of Controlled Trials. J Strength Cond Res. 2016 Aug;30(8):2361-8. doi: 10.1519/JSC.0000000000001316. PMID: 26694507.
 Taddei UT, Matias AB, Duarte M, Sacco ICN. Foot Core Training to Prevent Running-Related Injuries: A Survival Analysis of a Single-Blind, Randomized Controlled Trial. The American Journal of Sports Medicine. 2020;48(14):3610-3619. doi:10.1177/0363546520969205
 Beattie, K, Carson, BP, Lyons, M, Rossiter, A, and Kenny, IC (2017). The effect of strength training on performance indicators in distance runners. J Strength Cond Res 31(1): 9–23.
 Blagrove, R.C., Howatson, G. & Hayes, P.R. Effects of Strength Training on the Physiological Determinants of Middle- and Long-Distance Running Performance: A Systematic Review. Sports Med 48, 1117–1149 (2018). https://doi.org/10.1007/s40279-017-0835-7