Body Weight Training May Not Be Enough

90 kg squat

Running helps clear my mind. It also has a wide range of benefits like boosting immunity so you are less likely to fall sick. In fact, even 10 minutes of running at really slow speeds can boost your cardiovascular health. However, other than your leg muscles, running is not so good at building your other muscles.

Hence, strength (or resistance) training helps strengthen your muscles and joints which can make you faster and more importantly, decrease injury risk. Research by Lopez et al (2021) suggest it really does help to lift heavy (whatever that means for you since we are all different).

28 studies (with 747 healthy adults) were reviewed. The researchers found that a wide spectrum of loads (or weight) resulted in very similar increase in muscle size. However, it was only with higher or moderate loads that resulted in a significant improvement in strength.

This means that using lighter loads (or weights) may help "grow' your muscle, but it's the heavier weights that will make them much stronger. These findings were more apparent for those new to strength training compared to those who have been strength training for a while.

Those who strength train regularly will benefit by adding more sessions to their routine than simply adding more load. 

One reason for strength increases by higher loads (weight) is greater neuromuscular adaptation (or signaling). Meaning the connection between the brain, central nervous system and muscles adapt to be able to recruit more muscle fibers and increase the frequency of them engaging. This improves coordination within and between muscles in ways that contribute to more force.  Hence you get more strength through increased firing frequency.

The authors suggest that those new to strength training do 2-3 strength sessions a week, performing 8-12 repetitions per exercise. Select a weight you can do for that many reps but feel fatigued at the end of the set.

Remember your strength training program should be based on your running goals (i.e to run faster) and needs. Do not afraid to lift heavy and if you need a trainer/ physiotherapist to guide you, make sure they know your need for injury prevention and not to get bigger.

Reference

Lopez P, Radaelli R, Taaffe DR et al (2021). Resistance Training Load Effects On Muscle Hypertrophy And Strength Gain: Systematic Review And Network Meta-Analysis. Med Sci Sp Ex. 53(6): 1206-1216. DOI: 10.1249/MSS.0000000000002585