We hear a lot about relaxed power in Aikido, but it is also the goal of most martial arts - they just come at it from a different point of view. Generating power is about using the power centres of the body through good alignment and timing to a single point of focus. (It then becomes good technique if this coincides with uke's weakest point in their body/balance).
Karate-ka (i.e. students of Karate-do) and practitioners of other striking arts have long since perfected the movement that generates maximum power for striking – that allows them to produce spectacular breaks of wood, tiles etc. (Incidentally the tensile strength of bone is stronger than concrete.) This power is achieved through very careful alignment of the body and striking limb at the instant of impact by a combination of factors including mass and velocity. A punch generated solely by a limb can have a certain power (such as a jab) but when it is aligned with a much greater mass such as that of the torso the power is much increased. So while a particularly strong limb might weigh 10kg it is small when compared to the mass of the torso of around 50kgs (subjectively in a medium sized male). Hence while a boxers jab is likely to cause injury – it is the reverse punch that causes the knockout delivering maybe 5 times more power.
To generate power we employ the kinetic/kinematic chain starting with the largest mass/power points and focusing this to a fine point. It is analogous to cracking a whip: all segments of the body are loosely coupled and slow movement at one end leads to power and speed at the hands.
Thus we draw power from the earth, some call this rooting (biomechanists know this as the ground reaction force) as we push against the ground, then through good alignment of the legs and knees this is sent to the power center of the body - the tanden. The tanden controls around 60% of the bodies mass and then transfers this to the arms and, hopefully, an uke.
In aikido we can also drop or sink into the ground, this can unleash power the equivalent of a lawn mower with very little effort (see 09 Tanden power for the maths )
Alignment of the feet in hanmi, with the centerline of the body (seichusen) and the hands is critical to preserving and generating the power. in Aikido we learn this through the taiso solo exercises and diligent practice with weapons. These exercises also help us to ensure our mind is on the job.
Once you can generate the relaxed power the next step is to transfer it effectively (03b Ki Power: Transferring) and then to apply the power correctly (03b Ki Power: Applying).