Sled towing is an accessory exercise used frequently in sprinting, American football, rugby, powerlifting and strongman training. Various attachments can be used for sled dragging. Around the hips, ankles, shoulders, with straps to include arm or shoulder work and some even wrap them around elbows and knees.
Lawerence, et al 2012 decided to see what the muscle activation patterns of sled dragging were. They recruited 12 college aged (8 male, 4 female) and have them drag a sled. The sled was calibrated to 50% of bodyweight for each participant and they walked at 1.3m/s. The attachment was either at waist level or around the shoulders. Hip extension moment impulse was 3-4 times larger with the waist attachment compared to the shoulder attachment. Knee extension moment was 2-2.5 times larger for the shoulder attachment compared to the waist attachment.
The ratio for hip to knee moments came out to less than 1 for the shoulder attachment- indicating it is knee dominant and greater than 1 for the waist attachment making it a hip exercise.
This is important since we know that the hip to knee moments for squats are 1-1.5 and for deadlifts are 2-4. This indicates that to assist with raw strength and power, using waist attachments will generate greater force than shoulder attachments.
As always, get proper equipment, get proper coaching, use your head and break into a new training modality slowly. Have fun, train safe.