I am often asked about loading of the knee joint by golfers at my site www.golfersknee.com. A common question is why does my knee hurt more with the driver and long irons. The answer is that the length of the club’s lever arm (length of the shaft) causes a greater centrifugal impact force.
The other question, even one today, is why does it hurt my knee more off the tee and in the fairway, than in the rough. The force of the swing is the same and the load is the same. However a similar shot and swing in the rough has a lower peak impact load since the load is taken up by the grass as compared to fairway or tee with driver.
The load is the same, but dispersed as the club head goes through the longer grass of the rough, so the peak load which is damaging or painful is greater where there is no damping of the peak impact force of the long grass. Think of a hammer hitting a wall of a swimming pool below and above surface. The force would be the same, but when swung under water there is less of a peak impact when the hammer hits the wall.