MariposasConcentric (Lifting) Phase
The concentric phase is the part of a rep where the muscle shortens under tension, producing force to move the weight against gravity. In a bicep curl, it's the upward pull; in a squat, it's the drive back to standing. This is the phase most people think of as 'the lift' itself, and it's where the most obvious power output happens. What many lifters miss is that the concentric alone doesn't build as much muscle as pairing it with a controlled eccentric. The concentric phase also tends to be the limiting factor in maximal strength efforts, which is why tempo prescriptions often focus on slowing the eccentric while keeping the concentric explosive. Understanding this phase helps you train with intent rather than just moving weight from point A to point B.
Example
During a bench press, the concentric phase begins the moment the bar leaves your chest and ends when your elbows lock out at the top. Many coaches cue lifters to press explosively through this portion because recruiting fast-twitch fibers during the concentric translates directly to strength and power adaptations over time.