A year ago, The Grocer described the category as a "phenomenally vibrant area driven by changing lifestyle" with sales soaring 15% to £683.2m.
However, one year on, category value sales are up just 3.4% to £706.8m with leading brands Lucozade and Red Bull taking heavy hits on some lines.
Lucozade Energy remains the market leader, but sales have dropped 1.6% to £226.7m , with Hydro Active down an alarming 30% to £5.8m.
Sales of the second biggest player, Red Bull, were up just 0.1% to £178.2m, marking a significant slowdown from the 10% jump of the previous year.
Both brands blamed the recession for the sales slowdown.
"The current financial climate has meant there have been fewer opportunities for growth this year," said Red Bull, while GSK claimed the economic climate, was "influencing consumer shopping habits."
Relentless was a rare success story for the category, with sales leaping 31% to £48m, which CCE credits to the launch of Relentless Shots in July.
The continuing growth of Relentless suggested tough times ahead for Red Bull and Lucozade, said industry sources.
"Lucozade and Red Bull now seem to be follower brands witnessed most recently by Relentless getting in first with its energy shot offer," said Kate Waddell, MD consumer brands at Dragon Rouge. "Previously, both held their own: Red Bull being confident enough to be simply the 'inimitable' Red Bull and Lucozade innovating with Hydro Active and other new offers."
Martin Jeremy, co-founder of My Goodness Shakes sports drinks claimed the slower sales were the natural result of the category maturing.
"New entrants to the category have not added anything new and brands are now competing against each other for market share rather than creating incremental sales."