I did not read all the posts, so this may be a repeat of information.
First, the poster is requesting information on lifting a pack. All the criticism for carrying 40 pounds is not helping the poster figure out how to lift the pack!
In the old days (1960's) our packs were always heavy with the old heavy gear and add food for 15 days and climbing gear and we always carried 60 pounds. Here is how we did it.
First, find a spot if possible where your pack can sit uphill from your feet. This helps but is not absolutely necessary.
Second, grab both staps and glide/lift the pack up onto one bent knee.
If you loosen the pack straps a bit (but not too loose) the next step is a bit easier.
Third, once the pack is balanced on your knee, keep holding the right strap with your left hand (right strap is the one that ends up on your right shoulder) , release your right hand from the left shoulder strap, twist slightly as you insert your right arm into the right shoulder strap, remaining a hold of the strap with your left hand and the pack weight on your knee.
Fourth, use your right elbow to shove the pack to the right as you shift the weight of the pack from your knee onto the right shoulder. This is one smooth move. Stand up and unbend your knee.
Fifith, reach behind with your left hand and find the left shoulder strap. Insert your hand and arm and get this on your shoulder.
Sixth, hunch shoulders and lift the pack up a bit as you buckle the hip belt.
Now tighten the shoulder straps so that most of the weight is on your hip belt but some on the shoulder straps. Clip the sternum strap and adjust.
This definetly works better with the old external frame packs but I use this method on my interal frame pack too. Use your legs and knees. Do not bend and pick up the pack with bent back.
I am about 115 pounds and picked up packs weighing up to 100 pounds this way (carrying out an elk).