Training sudden issuance of force can be broken into two components. One part focuses on the flow of power through the arms and the other of power from the body.
The arms must be soft yet retain tensile strength like a coiled, twisted cable. In this way the force generated is fast, fluid and stinging.
The force from the body must be sudden and forceful like a raging, charging bull. In this way when your body impacts your training partner it will fling him away, rather than push him away which requires more strength.
To do this you must maintain a degree of resiliency in your body structure so that the force can be whipped out and not pushed out.
When you are very familiar with the nuances of the movements you can progress to minimizing your external movements and start to apply more intention into your force issuance.
An example of this is the use of Ward-Off at 2:00 and Push at 2:41 in the clip; both of which in this case used of peng jing which is a vertical circular force. This is illustrated below using a drawing from a chapter in the unpublished TaijiKinesis Vol 2 which explains one of the force components trained in Grasp Sparrow’s Tail.