Are Arsenal and Liverpool the Premier League sides most adept with their use of substitutions?

With the impact off the bench never greater – last season, subs accounted for a sixth of all outfield playing time at some clubs and contributed a record 133 goals – the benefits of mastering changes are clear. The impact of Jhon Duran for Aston Villa this season is a further example.

And with all teams searching for marginal gains, it might not surprise you to learn that there is now specialist training for subs to ensure they are ready for whatever the game has to throw at them when they enter.

The BBC Football Extra newsletter this week spoke to Sammy Lander, who has pioneered the role of “substitutions coach” within English football. He started at AFC Wimbledon before going on to consult clubs at Premier League and international level.

Of the sides who are gaining from the most from their subs, Lander said: “Arsenal have been very successful in using their substitutes in drawing game states and often have a high number of points achieved from this game state with substitutes on the pitch.

“Across the last three seasons, Liverpool are quite comfortably clear as the team who have registered the most goal contributions from substitutes while Newcastle are fairly positive and consistent with impact across all game states, as are Brentford.”

But what does a substitution coach do?

“A common misconception seems to be I just tell the subs when to go warm up – I wish it was that easy,” he said. “In reality, my week consists of ensuring our substitutes feel tactically, technically, socially, physically and psychologically ready.

“Having players accept their role is a massive step – then, you can start to add layers that are physical, social, technical and tactical. Substitutes are often very reactive to the questions the game is posing, so having them ready for every possibility is important.”

With players better prepared for their role, Lander says the in-match process is then akin to a card game.

“I perform a vast amount of in-game opposition analysis, looking at the granular details and trying to prepare every eventuality in what I refer to as my playbook,” he said.

“This means having the right substitute – not always the best – ready for if that situation arises. Once we know the probabilities of these situations, I can start preparing processes that can prepare the substitutes for these.

“I liken the process to Top Trumps. Once your opponent makes a move, every card is beatable – but you just need to know your pack, the game, and then the appropriate card to choose and when to place it. A similar approach is what I take with substitutions.”

And is the role of substitute now one with greater cache? Lander thinks so.

He added: “Rugby union coach Eddie Jones coined the term ‘finishers’ instead of substitutes and this was a huge progression, challenging the negative stigma that is typically associated with the word ‘substitute’. We have added layers to this by introducing the term ‘what finisher are you going to be?’

“We introduced tactical roles with psychological names. Therefore Jorginho at Arsenal might be a controller, a smoother, or a closer. Certain teams, depending on their tactical style, will require different names.

“All these names have a definition that allows for you to add process and identity to a substitute role, but also add direction and alignment.”

And will we see players emerge who are purely specialist substitutes?

“Sometimes a player’s profile might be more effective as a substitute and it’s about recognising this and implementing in the right format – the when, how and where,” Lander said.

“A little more frequently, my role is spent trying to help players produce their starting statistics as a substitute.”