Like many people, I've been been playing a lot of Black Ops lately. A little too much, perhaps. When you smear yourself in camo paint and start looking for decent camping spots on your way to the bus stop, you know you're overdoing it.
But even though I've enjoyed playing the game, I've noticed is the multiplayer action doesn't set my pulse racing quite so much as Modern Warfare 2 did. I mean this quite literally. A MW2 session would leave my heart pounding, my pupils dilated and my adrenaline levels off the chart. And don't even get me started on the mood swings.
We like to pretend it isn't so, but playing games can really make your blood boil. Whether you're attempting to post a perfect Pac-Man score or getting noob-tubed online by some pre-pubescent Americans, gaming can be a stressful experience.
But just how stressful? What are the psychological and physiological impacts of engaging in our favourite pastime?
Before you throw your hands up in disgust as yet another article tells you how bad playing games is for your health, let me state that I'm an avid gamer. I love playing them, I love talking about them and I love writing about them.
I'm not about to tut at you for wasting your time playing games, or suggest you're liable to kill your pet tortoise with a potato masher if you put in too many hours with a first-person shooter. I'm interested in why certain games get our pulses racing, and why the physiological effects they generate make them enjoyable and even addictive.
Imagine a scene similar to Ivan Drago's training camp in Rocky IV. I'm flanked by scientists in white coats and banks of humming machinery whilst playing some of the gaming world's recent releases.
Or, imagine a lounge, an Xbox 360 and an off-the-shelf heart rate monitor. This isn't meant to be high-level science - it's about investigating why some games set our hearts thumping while others leave them cold.
The weapons of choice for this experiment were blockbuster shooter Black Ops, football behemoth FIFA 11, the super fast arcade street racer Split Second Velocity and zombie thriller Left 4 Dead 2. The aim in picking such a vast array of titles was to find out if different game types had a different impact on my body.
I have a resting heart rate of around 60 bpm. It's about average and would be a lot lower if I spent my time in the gym rather than experimenting with the physiological effects of games, but there you go.
I wanted to find out which game would have the biggest impact on my ticker - whether driving cars would set my pulse racing faster than beating zombies to death with a cricket bat, for example. Here's I found out.
Disney's eye-popping racer was the first game I booted up. The impact was immediate. In the heat of a race where high speeds, exploding cars and general hairpin tomfoolery were the norm, there was a 15 per cent increase in my BPM.
Not much to write home about. But as the races got harder my heart pumped faster and faster, consistently clocking up an average increase of between 15 20 per cent. There was even the odd spike, with a couple of 30 per cent-plus rises coinciding with those races where I repeatedly crashed into the barriers and flung my controller across the room.
Left 4 Dead 2
After taking a time out and letting my heart rate drop back down to its usual state, Left 4 Dead 2 proved to be somewhat of a disappointment. Overall the increases were negligible, save for the occasional zombie horde which would cause a spurt in adrenalin levels and a subsequent 15 - 22 per cent peak in my BPM.
It's the type of pattern that you'd expect to find whilst watching your average scary movie, with peaks and troughs revolving around the action on screen.
Call of Duty: Black Ops
Feeling somewhat underwhelmed by the previous two experiments, I hoped Treyarch's smash hit shooter would give me some more interesting results. While playing Split Second and Left 4 Dead 2 I'd learned that violence and tension seemed to have a direct impact on my heart rate. I was optimistic these elements would come together in Black Ops to spectacular effect.
Within moments of getting stuck into the single-player campaign, the numbers started to go off the chart. The monitor began beeping away: 81 BPM, 86 BPM, 91 BPM... The numbers peaked at around 95 BPM - around 50 per cent above my resting heart rate.
They were consistent, too. No matter which game mode I played the figures stayed high, providing the sort of prolonged increase to my heart rate you might experience whilst taking a brisk walk.
It took just one end-to-end match on FIFA to really get my heart rate up and keep it there. Over the course of a couple of hours of play, complete with dirty tackles, some absolute screamers and a few dodgy refereeing decisions, there was between a 40 and 50 per cent increase in my resting heart rate, on average.
There were also plenty of spikes which coincided with the tension of a competitive match. In other words, my heart reacted in exactly the same way it would during the highs and lows of a real game of football.
A note about online play
The real eye-openers were reserved for when I went online. Even as I sat in the pre-game lobbies with conductive pads on my chest and notebook at my side, my heart rate started to creep up. It seemed that simply the anticipation of pitting myself against real-life opponents was enough to get my juices flowing.
But that was nothing compared to what happened when the action kicked off. Playing both Split Second and Left 4 Dead 2, I recorded highs of 93 and 89 BPM respectively. It seemed like the constant tension involved with facing off against my peers was doing the trick in a way that the solo action just couldn't achieve.
FIFA produced similar results. I consistently racked up 50 per cent-plus increases to my resting rate. The frenzy of a Black Ops firefight pushed my heart even harder, with several recordings reaching well over 100 BPM.
Aside from the strain the games were putting on my heart, I also noticed that my little online session had caused a few physical side effects. Whether it was a result of a prolonged day of digitised action or simply the flood of adrenaline coursing through my system, I was noticeably twitchy once I'd laid down the controller for the final time. I even had a touch of the shakes.
What does it all mean?
All I can tell you is that the more my heart rate shot up, the more involved I was with the action and the harder it was to tear myself away from my machine. Luckily Professor Mark Griffiths, director of the International Gaming Unit at Nottingham Trent University, was on-hand to help me make sense of it all.
Griffiths is something of an expert on this subject - so much so that he was called to talk about why games were addictive on that Panorama special. The programme aired, as fate would have it, right in the middle of my own experiments.
Turns out my elevated heart rate was a result of my body being flooded with adrenaline and endorphins, due to the sheer excitement of the games. "Increased excitement and arousal can become very physiologically rewarding for players," Griffiths said.
"This may be part of the explanation why some people become addicted to video gaming as they are addicted to the chemicals, such as the morphine-like endorphins, that the body releases in states of high arousal."
Simply put, the more engrossed I was in the action the more excited I got, and the more of these chemicals my body produced. It was these chemicals that were contributing to my enjoyment of the experience and made it harder for me to tear myself away from the action, as I wanted more of them.
This is similar to the situation experienced by gamblers or, to a lesser degree, extreme sports enthusiasts. Enjoyment of their pursuit comes from their physiological reaction to the excitement, risk and reward of their exploits.
But why the increase in heart rate when I went online? Traditionally we've played games for the rewards, whether that's improving our high scores or completing the story. But playing online we experience what the Professor calls the "partial reinforcement effect", where our rewards are intermittent.
Here, there is no definite conclusion to the experience. This potential to play on endlessly means we get drawn into the "just one more go" cycle. We keep playing in the hope that the next reward or achievement will be just around the corner.
So does this mean we're all addicted to games? Well, despite what some of the scare stories in the mainstream media might have you believe, no. "Playing excessively does not mean someone is addicted," said Griffiths.
"Games can be immensely rewarding and psychologically engrossing, and for a small minority of people, this can lead to addiction. Most of these addicted individuals have susceptibilities and vulnerabilities which when combined with the structural characteristics of the game itself can lead to addiction in a minority of cases."
There is a serious point here. Despite the inherent susceptibility of the unfortunate few who are on the slippery slope to addiction, surely the industry has to take responsibility for the potential impact of its products?
After all, designers know exactly what they're doing when they're building this aspect of engagement into the game. Perhaps, as with the the alcohol and gambling industries, the onus should be on them to warn gamers of the potential dangers of using their product.
What of the rest of us, those who can spot the fine line between addiction and excessive enjoyment? Games can be a wonderful thing. They can give people purpose, they can bring people together and they can be a hell of a lot of fun. But the moral of the story, as you might have spotted a few paragraphs ago, is to enjoy games in moderation, and know when to stop.
Now leave me alone, I need another 8000 XP to unlock an AK-47.