In a general sense there can be no absolutely accurate ‘traction-force calculation’ since most mechanical attributes patient to patient are unknown. However we have to make assumptions and these are based on both morphology, function, patient condition and duration of pain. It makes sense to “limit the liability” in ALL cases, however limiting the pull force (tension) in ALL cases could let patients needing robust, high-force procedures to slip through “underserved”. The more ‘Acute’ the condition the lighter the pull. Acute both in temporal-terms and level/intensity of pain. Since most moderate or severe LBP (or neck pain) is indubitably a SPRAIN or annular compromise overstretching it early on is utterly counterproductive. The VAX-D protocol called for a 3-4 week “cooling off” period where “real/traction-able/traction-responsive” conditions were allowed to simmer…becoming more apparent after several weeks of natural de-inflammation/healing. After which, persistent symptoms gave a green light to decompression. The more chronic the symptom the more relavant higher force MAY be…but as discussed before; degenerative disc fibers are not infinetly adaptable to stretch, and can sustain injury if overloaded. And that could mean prolapse in the worse scenario.
We seem to agree 30-35% TBW is a good starting point for sub-acute/chronic conditions whose symptoms are LB with or without some pelvic/thigh referral. Sub-acute is typically likely at least 2-3 weeks since onset. Acute presentations (you feel compeled to decompress) its best to stick to 20-30% TBW with a TRAC-short pull (10-15 secs pull/rest, 5-8 min). IF it’s a compromised condition you probably will not have crippled them too badly.
I routinely say: “don’t be dogmatic about high force OR low force”, our rules are guide posts. There are many patients (yes typically big men) who do require (or demand) serious force (90-120 pounds) however more patients require less force and are better served at 30-35%.