About the twitch speed of those fibres: in age-related muscle decline, fast-twitch muscle fibres diminish at twice the rate of slow-twitch fibres. Putting the brakes on muscle breakdown effectively preserves fast-twitch fibres, meaning you won’t be the one asking the Bunnings guy to carry the potting mix to your car. Consider heavy strength training, rapid reps with light weights and plyometric moves your little-old-lady prevention strategy.