Fitness plus not working

Ok, i can use the fitness plus fine on my phone, its paired with my watch, when i use the HMDI lead to use with my TV (i have the apple tv within my LG tv) and i can see the previews fine on my tv, then as soon as i go to start working i get the 3,2,1 on my tv screen, then when the workout starts, the screen goes black and i only get the sound from my tv.

I called appal support yesterday and spend an hour on the phone, really helpfull lady, she was telling me how the HMDI lead should work, she was going to pass me on to tec support, but was having problems with her phone, she was going to call me back, but didn't!! any help via here???