I've actually owned these for a year.  Work muscles at home with door jam attachment and pack for wintering away from home.  I've worked with a trainer ~ these bands fill in just fine when needed.  I thought they might stretch out of shape but that hasn't happened.  I'm focused on upper body strength to ward off further loss of bone density.  Pro-active for strength seems like the a good plan.  I've been happy with Black Mountain Resistance bands.  I use these bands twice a week.