Average temperatures in Houston in July and August reach 93.5F (34C), with a peak in July last year of 98.6F (37C).
That is not stifling heat compared to some countries – or even other US cities, with the needle in Las Vegas regularly reaching 115F (46C) this month. But the bigger issue, says Clarkson, is the humidity.
“It’s an absolute killer,” he said. “You could be losing between 5 and 10 lbs every training session just through water loss.
“So weighing in, weighing out, and recovering when you get home, is really important.
“I’m a huge believer in training at the intensity we want to play at. So even if we have to reduce the time, when we’re actually doing something, we want it at full speed and recreating that match intensity.
“The challenge we face in the summer, because it is so hot, is that if we’re on the field at 10.30am it becomes ridiculous, you can’t do anything.
"We have to be on the field and started by 9am. We’re then finished by 10.30am and that’s when the heat and humidity really kicks in. You don’t want to be outside from 11am to 6pm in Houston.
“Part of the problem with that is when we do a recovery day, the day after the game, they’re leaving the stadium by 10pm and don’t get a lot of sleep if we’re getting them up early again on Sunday."
"It's about managing the individuals. Everything we do, we do it with a ball..."
Of course, heat and humidity – and the ability to cope with it – is all relative. Wherever you live, you become accustomed to the most common weather conditions.
But heatwaves strike everywhere, to varying degrees – so how can teams cope when the temperature goes into the very deep red?
“It’s important to not be fixated on training for an hour and a half, or two hours, whatever it is,” said Clarkson.
“Just because you’ve got that time, it doesn’t mean you necessarily have to do that amount of time. It’s about managing the individuals.
"Everything we do, we do it with a ball. We hardly do any just pure running. By having a ball in there, there’s that extra motivation – players will work even harder because there’s a ball there.
“Hydration is vitally important, but if you’re having to catch up while you’re in the training session, it’s too late. Preparation for the players in terms of hydration is vitally important – that has to happen leading up to the training and then recovery is vitally important as well.
“The key to it is the amount of time you’re out there, what you want to work on, having a plan and sticking to it.”