Stephen Keane | Online personal trainer on Instagram: "Ok, it’s not just weight × moment arm, it’s force. Force = mass × acceleration. So yeah, speed of movement plays a role in how much work is done. Plus how large a range of motion you go through. But I’ve probably already lost half of you, haven’t I? So for the average gym-goer, just picture weight as a big rock… and remember there are some other rocks involved."