If you ever find a bottle of orange squash-infused-water behind a tree in the Magaliesberg, don't take it away: it might well have been put there by a local long-distance runner, and it might be helping him through a difficult training run.
"If you're getting tired of training or racing," says sports scientist John Brewer, "having something sweet in your mouth can give you a mental or physiological boost that makes things seem a little bit easier. It's almost like your body is thinking, 'Hey, here it comes!'"
Brewer is one of the world's leading marathon experts and is full of tips like this. I'm grateful for them: he and I are discussing long-distance running over the course of a 6km jog and as he scampers nimbly up a steep hill it's becoming increasingly difficult for me to keep up.
No shame there: he's 56 this year, but he's a professor of applied sports science, a former adviser to the England football and cricket teams and a 19-time London Marathon runner.
DECARB THOSE MYTHS
Brewer has just published a book in which he seeks to dispel falsehoods about running and explain to beginners of any age how they can improve their technique quickly and easily, especially if training for a marathon.
Think you need a good start to get a good time? Wrong: depleting your carb resources early is a terrible idea.
Reckon your training should include runs totalling 60km-80km a week? Wrong: for amateurs, shorter sprints and one long weekly run should be enough.
Think it's all in the mind? You can't outrun poor training, slacker. And if you think marathons are bad for you, that you need to improve your gait, and that you should eat a trough's worth of pasta the night before the race, then you're wrong, wrong, and wrong again.
But if you think running will lower your cholesterol, blood pressure and risk of various unpleasant illnesses, and also lose you some body fat, then you and Brewer are on the same page.
"If I can motivate people to run marathons, great," he says, "but if I can motivate a few people to do something shorter, then that's good as well."
TRUST YOUR BODY
It's a bright, mild day in the fields, warm enough for the leaves to still be on the trees but cool enough for it to be obvious that it's exertion, rather than heat, that's making me sweat. I shouldn't have worn cotton, Brewer says, because it soaks up moisture and becomes heavier; the lightweight fluorescent thing he's wearing would be better for a race.
Fortunately, we're not racing today, and now that we're on flatter ground I'm hitting a nice rhythm. What makes it all the more enjoyable is that at a time when I'd normally be in the office, I'm instead breathing fresh air under open skies.
"I'm a big advocate of running outside rather than in a gym," he says. "The environment changes all the time, so the trees will be a different colour, and often you encounter kites hovering and screeching."
He's a good coach, and while he disapproves of my breakfast - "Crisps and hummus?! I'd be generous to give you two out of 10" - he reassures me that my donkey-on-ice running style is all right. "Your body tends to know what is naturally right for it, and you're running in a way that's right for you."
And he has some good advice for how to cope with hitting the proverbial wall: "Just try to change your stride length, because there'll always be some energy in the muscles, and that'll start to find a few extra reserves of fuel that you haven't been using in your standard stride."
Even if you haven't run for decades, Brewer says you can work up to it. "Start with a walk, find a friend to do it with if you can, and build up gradually."
Citing champion octogenarians like Canadian Ed Whitlock - who became the first person over 70 to run a marathon in less than three hours, and died in March this year aged 86 - he says the veterans category will see plenty of records broken over the next few years; older runners, he says, are mentally stronger than their juniors.
"Do we stretch now?" I ask, as we reach the car and slow to a walk. "If you want to, yes," he replies, "I suppose, theoretically we should ... but we haven't been going very fast."
I'd better start training.
