Jon Lewis, England's bowling coach, has called on Ollie Robinson to work harder on his fitness, after the team's flying start to the fifth Test at Hobart was undermined by a back spasm that left them a bowler short for the final two sessions.

Despite being reduced to a four-man attack due to the side strain that has required Ben Stokes to play as a specialist batter, England dominated the first hour of the match in helpful conditions, with Robinson right in the thick of the action. He claimed the big wickets of David Warner and Steve Smith for ducks, and had Marnus Labuschagne dropped at slip on 0 as well, as he finished his first seven-over spell with figures of 2 for 15.

However, after returning to the attack straight after lunch, Robinson conceded two boundaries in a low-key over in which his pace dipped to 112kph/70mph, and though he remained on the field thereafter, he did not bowl another ball all day as Australia cashed in on a weakened attack through Travis Head's second century of the series, and a second fifty in a row for Cameron Green.

Speaking at the close of play, Lewis confirmed that Robinson had suffered a back spasm, but put the onus firmly back on the bowler to do what's required to maintain Test levels of fitness.

"These things can come and go," Lewis said. "We're hoping that, with treatment overnight, he can come back tomorrow and be free enough to bowl. So that was the reason that he stayed on the field for as much as he did, even though he wasn't moving as well as he could."

Robinson has met the requisite standards as a pure bowler on this trip - he is England's leading wicket-taker with 11 at 23.45, and now has 39 at 20.69 in his short Test career. But he missed the fourth Test with a shoulder injury, and also appeared to tweak his hamstring while stretching for a caught-and-bowled chance during England's third-Test defeat at Melbourne.

"It's something he's definitely looking at, and definitely we're working on with him," Lewis told BT Sport at the close. "If he's going to perform consistently over a long period of time at this level, he will need to be a fitter bowler, 100%.

"We've had those conversations, we've been pretty frank with him. And now it's up to him to go and do the work."

Asked how Robinson had responded to the demands from the coaching team, Lewis added: "So far, he has been okay." But, Lewis said, with England's opportunity for match practice hindered by the international cricket's biosecure requirements, the onus was on the bowler himself to put in the sort of fitness work that he has not previously required, given the regularity of his appearances in county cricket for Sussex.

"With our schedule, we've had a lot of cricket, and training and playing at the same time isn't always straightforward, even though we can do it," Lewis said. "That's something he's learning. In county cricket that doesn't often happen. The guys don't train and play together at the same time because they play game after game, after game. But in international cricket, he's on the road a lot, he's going to have to learn to look after himself better than probably does at the moment."

In Robinson's absence, England endured a bruising middle part of the day, in which they conceded 192 runs in 39 overs, with only the wicket of Labuschagne for 44 to show for it until Head holed out of mid-on, one ball after bringing up his hundred. Overall on a rain-truncated day, England conceded their runs at 4.05 an over, and Lewis was disappointed at the profligacy from an attack that had previously made Australia work for their rewards.

"In the middle session in particular, I thought were a little bit slow to adapt to what was happening in front of us," he said. "We could have bowled better. For long periods of time on this tour, we've controlled the rate of the game, and this is probably the first time that they've got away from us in terms of run rate, which is which is a shame because of the great start that we had."

Although the conditions at Hobart looked classically English at times, with a green pitch and heavy cloud all day long, Lewis insisted that the vagaries of the pink ball had been a big factor in Australia's fightback.

"We bowled fantastically well up front, and then we felt like movement went out of the ball completely after about 20 overs," he said. "They also counterpunched fantastically well with Marnus and Travis Head, so we've got to give them credit for playing a couple of very smart innings in the situation that they were in.

"But the pink ball is very different to the red Kookaburra, which is very different to the Dukes ball as well," Lewis added. "With these day-night games, the conditions change a lot very quickly, and the condition of the ball changes a lot. And the timing of when you're batting against a new ball and against a ball that isn't quite so new is really important."

Andrew Miller is UK editor of ESPNcricinfo. @miller_cricket