Tracing elite athletic performance

Materials World magazine
4 Aug 2014

How do you make sure a cyclist’s left leg is as powerful as the right, and why are fast bowlers stomping on force plates? Eoin Redahan asks the brains behind the Human Performance Laboratory in Salford.

Brian Clough was famous for winning two European Cups as manager of Nottingham Forest FC. He was also as mad as a box of frogs. Legend tells of a time when he used tree punching as a squad-building exercise. Another story has him sitting in a sauna in a full suit, sweating out the ills of an evening’s drinking.

For all the stories of Clough the manager, there are fewer about Clough the goal scorer. By the time he retired after rupturing his anterior cruciate ligament (ACL) at just 29, Clough had scored 251 goals in 274 starts for Middlesbrough and Sunderland. If only Clough had access to a high-performance laboratory back then. He might have retired with a 1966 World Cup winner’s medal in his pocket.

When good knees go bad
Footballers like Clough dread the moment when their studs root in the turf and their knee twists until the cruciate snaps. Sadly, these traumatic episodes will always occur, but at least scientists at the Human Performance Laboratory (HPL) in Salford, UK, can minimise the risk of ACL injuries using a combination of 3D motion analysis, force platforms and electromyography (EMG).

























Athletes in certain sports, such as basketball and football, are more susceptible to ACL injuries due to the amount of turning and jumping involved. While specific training regimes can strengthen the relevant muscle groups, it is worth knowing exactly how much an individual athlete is at risk.

The angle of the knees, hips and foot orientation serve as useful cruciate storm crows, from which analysis deepens. The HPL’s Christine Smith explains, ‘We use force platforms, which take kinetic and pressure measurements, and 3D motion analysis. We combine these with EMG and ultrasound. With surface EMG, pads are put on the muscles to pick up the amount of muscle contraction, so you can tell which muscles are contracting at a specific time and the strength of the contractions. When you put that together with motion analysis and force platforms, you start to build up a big picture. We then use ultrasound to look at the muscle and tendon architecture at a structural level.’

Armed with this intimate knowledge of the knee, coaches can stop frustrated footballers from premature returns to action. Steve Horton, Specialist Technician at HPL, adds, ‘When footballers are coming back from injury, we see if they are fully recovered or if there is a slight imbalance in their running gaits. We use a 3D motion capture system, with 12 cameras set up on a track. The athlete will have reflective markers put on the foot, knee, upper leg and lower back, and the cameras track the movement of these markers. The software creates a 3D model of the athlete, which helps us detect any imbalance in the running gait. If there is an inversion of the knee, we see if that was already there. We can pick up a variety of subtle indicators to tell us if an athlete hasn’t fully recovered and might need more rehab before going back into an intense playing situation’.

The aforementioned force plates are useful in the analysis of cricket bowling actions. Students at the HPL took a portable Kistler plate into the field and placed it on a low ramp (about 30mm off the ground) at the end of bowlers’ run-ups. Horton notes, ‘The bowlers ran in as normal, aiming to hit the force plate every time, and we measured the force through their leg. When you see what forces go through their joints, you see why a lot of fast bowlers have ankle and knee injuries. We also use high-speed cameras to get a slow-mo of the actual bowling action.’

Modified force plates are also helpful in weightlifting, a sport that is surprisingly technical. When most of us see the strained faces of the squat under weight of laden bar, we presume the sport is merely a matter of brute force. That, however, would do a disservice to both the bull-shouldered and the boffins at the HPL. Horton explains, ‘The FT700 ballistic measurement system is a modified weightlifting cage that has a simplified version of the force plate in the bar. Most of our force plates measure three axes – one vertical and two horizontal – but this one just measures the vertical force. It also has a distance transducer, which is essentially a cord attached to the bar. As the athlete lifts weights, we look at the distance the bar travels with the cord and the force applied (at each stage). From this, we can get a variety of measurements such as bar acceleration and speed. For athletes who have used the system and software regularly, it can improve performance and strength in training.’

Cycling is another sport with a technical underbelly that is seldom seen. Most will be aware of cycling’s soul-sapping, leg-burning exerts. The more ardent fans will know of the sport’s aerodynamic subtleties, but almost everyone presumes a top-level cyclist knows how to pedal properly. According to the Wattbike, almost everyone is wrong. The Wattbike is a bespoke (pun intended) exercise bike that contains load cells in each pedal to monitor efficiency.

Horton says, ‘Elite-level cyclists use cleats that are attached to the pedal, so they can generate a lot of force with the push down and the pull up. Now, if you’re a recreational cyclist, there will hardly be any force pulling up, but with training you can develop this extra force to give your cycling a boost. Not only does the Wattbike show the forces of the leg as it pushes down and pulls up, it shows the imbalance between the right and left legs. The force can be balanced through training.’

You’re a gas ticket
Of course, in sports such as cycling and long-distance running, the technical side often defers to fitness. When it comes to elite athletic performance laboratories, the first images that float to mind are of athletes running on treadmills in gas masks with plasters stuck to them, scientists in white trench coats nodding into their clipboards and, strangely enough, brands of isotonic drinks.

The reality isn’t too far removed from that, apart from the competitions between rival drinks (and maybe the clipboards). Gas analysers and treadmills are used to measure a runner’s expired breath during exercise. The analysers measure the oxygen, CO2 and the volume of air used to get an athlete’s VO2 max, which is the maximum amount of oxygen the muscles can use. In other words, it gauges a person’s fitness level. According to Horton, sedentary people will have a value of 30ml of oxygen per kg of bodyweight while elite athletes values will be 70–80ml. These markers prove useful as training guides. ‘Something else that is useful for endurance athletes is called the blood lactate threshold,’ Horton says. ‘Blood lactate (or lactic acid) is a byproduct of the metabolism. When too much of it builds up in the blood, it can lead to cramps and fatigue. We can measure the point at which it starts to accumulate in the blood, and we get the athlete to train just below that level. That level will increase with training, and the athlete will be able to run at a pace where the lactic acid doesn’t accumulate in the muscles and cause fatigue.’

While much of this technology is expensive, both Smith and Horton are excited about the falling costs of some equipment. Horton noted that the HPL spent £8,000–£10,000 on high-speed cameras six years ago. Now, digital SLR cameras can capture footage of your running gait at 300 frames per second for £500. To put that into perspective, normal video films at about 30 frames per second. It is not just the falling cost of equipment that is encouraging. ‘Devices are becoming more portable and they are maintaining their accuracy,’ Smith says. ‘At one time, a lot of our equipment wasn’t portable, so we didn’t have the ability to test things in the field. But you’re not getting a true impression of what’s going on. If you bring someone into the lab with the best will in the world, it is still an artificial environment.’

Nevertheless, many live to lament the real-world environment that halts dozens of careers each day. Brian Clough tried for two years to repair his ruptured cruciate, but played only three games more. And so he moved to management, where he won leagues and European Cups, punched pitch invaders and boasted with all the hot air he could muster. But he had no force plates to measure punches on trees, no gas analysers to measure expired fumes or swanky cameras to measure a cruciate’s snap.

What is a Kistler force plate?
HPL’s Steve Horton explains, ‘The Kistler plate is basically a lump of cast aluminium that measures force using a piezoelectric effect on quartz crystals. If you excite the quartz, it measures electrical voltage and that amplified voltage is proportionate to the force applied. That’s why they call them force plates.’

For more information on the HPL, email Christine Smith at