Before you take a step, your brain sends a message to your muscles - we're about to lunge, folks! - via nerve fibres that run down your spinal cord.

Muscles are made of bundles of fibres that contain two types of proteins. When given the green light, the proteins slide across each other, causing the fibres to contract. This motion moves the bones attached to the muscle, and you bob across the gym floor.

The lunge causes microscopic tears to the muscle fibres involved. To repair them, your body rushes healing white blood cells, protein and other fix-its to the scene. This increases the size of the muscle fibres and strengthens them. Ta da! Next time, you can add two more lunges to your set.

GET STRONGER

To get the most from your strength training, integrate cardio three times a week. A 2008 study published in the Journal of Strength & Conditioning Research found that, compared with women whose strength workouts stuck strictly to weights, those who ran on a treadmill for 30 to 60 seconds before each set gained six per cent more muscle strength, added nine per cent more muscular endurance and shed six per cent more body fat over 11 weeks.