To significantly increase endurance and strength without gaining muscle mass, practice a one-mile (1.6 km) walk/jog once a week while carrying a kettlebell weighing 30% of your body weight, switching arms regularly.

noli's read

This advice is similar to a form of 'kettlebell carry' or loaded carry, an exercise well known for strengthening the posterior chain, core stability, and muscular endurance. Physiologically, carrying an asymmetrical load intensely engages the core stabilizer muscles (obliques, transversus abdominis) to counteract tilting, which is validated by observational studies on functional training (Journal of Strength and Conditioning Research). The idea that this develops strength without major hypertrophy is consistent with the principles of strength-specific training (low volume, high intensity), as opposed to bodybuilding-focused protocols. However, the claim that this is the method to 'dramatically' increase these capacities is a generalization; scientific evidence supports the effectiveness of this exercise for core stability and resilience, but not necessarily as the sole vector of performance for all profiles. The risk of injury, particularly to the shoulder or back if the load is too heavy or the form is incorrect, is an important point of concern. There is a lack of randomized controlled trials (RCTs) specific to this precise protocol to validate its superior effectiveness compared to other strengthening methods.

the sources

1. 1Looney DP, Lavoie EM, Notley SR, et al. 2024
2. 2Puthoff ML, Darter BJ, Nielsen DH, Yack HJ 2006