Currently just 18.6% runners meet the recommendation of 2-3 resistance training sessions a week. Some endurance athletes have concerns about the risk of resistance training, but the data shows this to be misguided:

• There are 17.8 running-related injuries per 1000 hours of training for novice runners and 7.7 injuries per 1000 hours in recreational runners. [Videbaek 2015]
• This compared to 1.0-4.4 injuries per 1000 hours of resistance training, far below that of runners. [Aasa 2017]
  
  

The next question is whether or not it will actually improve, or even hinder, performance. Once again, the data bears out the idea that it is worth your while:

• A study by Beattie et al from 2017 found that after a 40-week strength training intervention, runners who participated in a strength training program performed better than their control group peers, despite the program producing “no significant changes in body composition variables between or within groups.” [Beattie 2017]
  
  

While this should already be enough to make a reasonable data-driven argument for the inclusion of weight training in an endurance athletes programme, there are also relevant benefits to be had in regard to pain mitigation and general health:

• For patellofemoral pain syndrome, a meta-analysis from 2018 demonstrated that strengthening of the hip and knee was superior to strengthening of the knee alone for treatment. [Nascimiento 2018]
• Beyer found that eccentric and heavy slow training produced improvements for Achilles tendinopathy. [Beyer 2015]
• Kongsgaard et al had shown the same benefit for heavy slow resistance training for the treatment of tendinopathy in patients with patellar tendinopathy as well. [Kongsgaard 2009]
• The use of Nordics has been shown to reduce the risk of strains, with an impressive number needed to treat (NNT) for preventing an additional strain of just 3. In this controlled trial, the cohort participating in the Nordic hamstring protocol suffered 3.8 injuries per 100 player-seasons, versus 13.1 per 100 player-seasons in the cohort that did not perform Nordics. [Petersen 2011]
• Resistance training is generally accepted to increase bone mineral density in athletes. Bemben 2011, [Mosti 2014]
  
  

Hopefully this makes a compelling case to get into the gym and hit the weight room, regardless of whether you desire the bulky aesthetic - there are many other important perks.