There's no need for the green screen. In fact, I would suggest shooting the 150kg weights in the same room and the same location as your finished shot. Since they're not moving, you can very easily mask them out and use that without worrying about green spill, lighting being off, and incorrect reflections.
Alternatively, shoot it practically with people helping your friend lift and then paint them out later. Make sure to shoot a clean plate!
150kg = 331 lbs, btw for any other Americans reading this
Planning is how you make this shot work, the compositing is easy. The perspective change as the weights are lifted is going to be the hardest part. Here's what I would do to match the perspective changes. Shoot your friend lifting the bar with half the wight on the bar, then do it again with the other half of the weights on the bar but position them so they are where they would be if all of the weights were on the bar. Then stabilize the footage so the bars don't move by tracking the ends of the bar and using stabilize motion. Do this to both shots, then line them up as best you can, use time remapping to match the timing, draw your masks and animate them to add both sets of weights to the bar. Once this composite looks good, re-introduce the motion to the shot using a null and parenting. Here's a short tutorial on how to track, stabilize, add something to the scene, then re-introduce the motion to the scene:
Wow both great ideas I will try them out both and see which works best. Thank you for the advice guys