The upper arm, lower arm, femur or upper thigh, and gaskin or lower thigh, are all equal in length. These are the levers that provide propulsion, and the smoothest, most efficient propulsion is provided by levers of equal length. The scapula is generally not as long as these bones, as it is not a true lever. It pivots on its centre point, being pulled forwards and backwards by massive layers of muscle across its entire surface. It is more important that it be wide, to provide roomy attachment for those muscles.
Short forelegs are less vulnerable to injury, but they are less effective at propelling the body.
Very long legs are a feature of racing dogs, but are much more vulnerable, particularly in jumping. The medium length leg is the best all around compromise for speed, strength and propulsion. The pastern is only slightly angled. The more angled it is, the less absorption it has, a bit like soft shocks on a car. A strong pastern has great absorption, but can also generate propulsive energy.