Rio Ferdinand says he has missed "the chemical that comes out of you" in professional sport as he launches a new career as a boxer.
The 38-year-old announced on Tuesday that he is to try his hand in the ring with the view to challenging for a belt over the next 12 months, just two years after retiring from football.
Although the former Manchester United defender insists he does not expect to progress as far as global title bouts, he is eager to experience the thrill of competition and to test himself "as a human being".
"A lot of people sit and watch huge fights, plus other sporting events and say 'I can do that' or 'they've messed it up'," he told Standard Sport.
"There are a lot of armchair fans wanting to pass judgement. Well, I'm going to walk the walk and actually do it.
"I'm into keeping fit and one of the big things I have missed since retiring from football in 2015 is the competition, whether it be as a team or as an individual going one-on-one against a striker.
"I just miss that chemical that comes out of you. I have not been able to replace it. This is a great way to get that back.
"I'm doing this for many reasons. I'm doing this to test myself as a man, as a human being.
"Can I change sports? Can I be a respectable performer in other sports? Can my body get through it?
"Can I mentally get up early at 5-6am in the morning when it is dark and cold to go on long, dirty runs? Then get back, take my kids to school, go to the gym and eat properly all of the time.
"This is a test of my mind and body, that's the way I'm looking at it. I'm not looking at it to become the world champion, I'm not stupid."
|Gascoigne hits back over Scottish Hall of Fame snub|
|NBA 2018-19: LeBron closing in on Jordan, Curry chasing Miller and Allen|
|Ter Stegen should start ahead of Neuer for Germany – Matthaus|
|England´s Sterling impressed by Sancho´s work ethic|
|Vandoorne seals switch to Formula E|
|Halep to end 2018 as world number one|
|Sri Lanka´s Jayasuriya charged by ICC with breaching anti-corruption code|
|Vermaelen out for six weeks with hamstring injury|
|LeBron and Irving did not fall out, says ex-Cavs trainer|
|Ramsey out of Wales´ clash with Republic of Ireland|
|Bolt angry with drugs test|
|Bad luck is not a coincidence – Kimmich concerned by Germany form|
|Mahomes: Chiefs need to win like Brady and the Patriots|
|Schuster warns Real Madrid not to panic-buy striker in January|
|We´re here to win! - Paine not happy celebrating a draw|
|Injured Thauvin out of Germany clash|
|Southgate hits out at early Premier League start|
|Modric to Inter talk is ´fantasy´, says Guardiola|
|Pats hand first loss to Chiefs after wild shoot-out|
|Cowboys, Ravens dominate as Pats beat Chiefs in NFL classic|
|Brady becomes first QB to 200 regular-season wins in NFL|
|Red Sox level series against Astros|
|Mbappe leaves red-faced Dembele on his backside|
|Red Sox ace Sale admitted to hospital with stomach illness|
|From UFC to NFL? McGregor throws pass for Cowboys|
|Ancelotti praises ´dangerous´ Mbappe|
|Uncapped Papalii named in All Blacks squad|
|Kane would star in LaLiga – Ramos|
|Guardiola unsure about Man City´s Champions League chances|
|Dzeko: Premier League return? You never know|
|Gurley dominates to help Rams beat Broncos|
|Butler expected to play Timberwolves´ opener against Spurs|
|I´m no wizard – Mancini asks for patience with Italy|
|The Messi and Ronaldo era is phenomenal – Guardiola|
|Dolphins defeat Bears in OT with 47-yard field goal|
|Almirola picks up win at Talladega|
|Wigan´s Sarginson wanted Grand Final glory in memory of brother|
|McLeish: Scotland keep shooting themselves in the foot|
|Sarries´ walking wounded a concern for Jones|
|Poland 0 Italy 1: Biraghi seals last-gasp win to keep final-four hopes alive|
|Seahawks top Raiders with blowout win in London|
|In-demand Hogg hints at Glasgow exit|
|Holder calls on Windies batsmen to step up after India whitewash|
|France´s World Cup win hurt me - Koscielny retires from international football|
|Bailey performs U-turn on Jamaica call-up|
|Evans becomes Buccaneers´ all-time leading receiver|
|Overlooked Alba is one of the world´s best, says Ramos|
|Del Potro a major ATP Finals doubt due to fractured patella|
|Gomez to replace suspended Stones for England|
|Luis Enrique applauds ´adaptive´ Southgate|
|Pepperell holds off Bjork for wire-to-wire British Masters glory|
|Steelers´ Shazier returns to Bengals´ stadium for first time since injury|
|Scotland 1 Portugal 3: Santos´ side pile misery on McLeish|
|Falcons prey on Toulon, Vunipola brothers injured in Sarries win|
|N´Golo Kante is fundamental for France – Lucas Hernandez|
|Real Madrid star Bale withdraws from Wales squad|
|50 Cent to meet Khabib for Bellator talks|
|Drink-driving charge does not change who I am – Lloris|
|Pavard backs Varane to beat favourites to Ballon d´Or|
|Gareth gives players more input - Henderson explains Southgate, Klopp contrast|
|Stephens qualifies for WTA Finals as Svitolina sits out Kremlin Cup|
|Disrespectful critics are treating us like amateurs - Hummels|
|Final Proteas-Zimbabwe T20 washed out|
|Deontay Wilder apologises for punching mascot on live TV|
|Irrepressible Djokovic hunting year-end number one|
|Henry has everything to be a success at Monaco – Deschamps|
|Shastri: Shaw plays like Tendulkar, Sehwag and Lara|
|Germany lose Boateng for key France fixture|
|Giorgi eases past Alexandrova to Linz title|
|Why not? I hope so - Lukaku harbours Serie A ambition|