Ultra-marathoner Andre Blumberg puts in 15 to 20 hours of training each week on tracks and trails around Hong Kong, his adopted city for the past 12 years. But for the German, it is the time spent at rest that is exhausting.
On most nights, Blumberg seemingly slumbers at 9,000 feet (2,743 metres) above sea level, where the thin air makes sleeping difficult. But while most athletes travel for hours or even days to get to such high and often remote terrains to live and train, Blumberg has a hermetically sealed altitude tent in his Mei Foo apartment.
This hypoxic, or low-oxygen, tent has a generator that pumps in a predetermined mixture of low-oxygenated air while removing carbon dioxide, recreating the conditions of "living high and training low". This forces the body to produce more oxygen-carrying red blood cells and may lead to better endurance when performing workouts at sea level.
"It takes some time to get used to and, initially, I found myself waking up during the night," says Blumberg, 43, the IT director of a power company.
The tent costs about HK$37,300. Its altitude can be adjusted slowly as the body adapts, with the generator able to simulate up to 21,000 feet (6,400 metres), slightly higher than Camp II at Mount Everest. Hong Kong's highest peak, Tai Mo Shan, is only 957 metres.
It has proven a valuable training tool for Blumberg, who is in the midst of attempting the Grand Slam of Ultrarunning, a series of four 100-mile (160-kilometre) trail races in the US over 10 weeks. This past weekend, he completed the second leg, the Vermont 100.
"Since I don't have sufficient time to live at and acclimatise to altitude, I use altitude simulation to get used to the added exertion and stress that I will experience during races," he says.
The concept of sleeping in altitude chambers or training with altitude simulators is not new, with the US Navy SEALs and professional athletes among users, including US swimmer Michael Phelps and British triathlon world champion Jonathan Brownlee.
But lately, such equipment has become more accessible. In Asia, Hypoxico, a producer of high-altitude training equipment, has had clients from the region, particularly Hong Kong, Japan and South Korea.
A basic home unit, which consists of an Everest Summit II hypoxic generator, deluxe queen-sized bed tent and a workout kit, starts at HK$27,200.
"We can safely simulate up to 6,400 metres with the knowledge that if your SpO2, or blood oxygen saturation, levels go to unsafe levels, you can simply step out of the tent to sea level conditions," says Hypoxico vice-president Matthew Eckert. His customers, aged between 12 and 79 years old, typically see improvements after three weeks.
Conventional high-altitude training - the concept of "live high, train high", and returning to sea level for competition - has its drawbacks.
"The adaptation period is rather long," says Lo Ka-kay, senior sports science officer at the Hong Kong Sports Institute.
"Some athletes may suffer from headaches, diarrhoea and insomnia if they cannot adapt well. It may be necessary for the athletes to decrease their training intensity and this may result in them being detrained when they return to sea level.
"Furthermore, the athletes may suffer from the detrimental effects of chronic hypoxia, such as muscular mass loss, fatigue or deteriorated aerobic performance," Lo adds.
Increasingly, athletes have been switching to the "live high, train low" approach. The method has been adopted by most athletes at the Hong Kong Sports Institute since 2005, with some demonstrating significant improvements in endurance and VO2 max, or maximal oxygen consumption, tests.
"Living at altitude brought about significant increases in red blood cell mass and also haemoglobin concentration," Lo explains. "Simultaneous training at a lower elevation allows these athletes to achieve running velocities similar to their sea level running velocities, inducing beneficial neuromuscular adaptations."
Some researchers are unconvinced of the benefits of altitude training methods, arguing the competitive edge is more mental than physical.
A recent study by Swiss researcher Carsten Lundby found no difference in blood measurement or performance between elite cyclists who spent 16 hours a day in altitude rooms and those living at sea level.
"Although scientific research on the topic produces mixed reviews, many coaches still believe in it," Hong Kong rowing coach Chris Perry says.
"Different athletes take different times to adapt, so it is best to go to altitude to check how each athlete will respond."
The Sports Institute is now modifying a room in the athletes' hostel into a hypoxic room, and will unveil a nine-storey building with two hypoxic rooms later this year. Also, the institute sends its athletes on stints to the mainland. France and New Zealand.
Thinking of gaining a competitive edge? Here are several options available to simulate high altitude training conditions of 1,300 to 2,500 metres in your home.
Altitude chamber This device uses generators to simulate a high-altitude environment within an enclosed area, allowing the athlete to run on a treadmill or ride a stationary bicycle while breathing in a mixture of low-oxygenated air. A typical unit costs about HK$27,000.
"One of the benefits of using such training options is the ability to train anywhere," says Hong Kong runner Yeung Yat-hung, who trained at altitude in Yunnan province for two months last year. "With altitude simulation, I can train at a specific elevation to achieve more effective results."
Pure Fitness introduced Asia's first high-altitude chamber in 2004, but it was in operation at its IFC outlet for fewer than two years. "At the time, training in a hypoxic chamber was believed to greatly enhance performance, especially for endurance athletes," says Marco Ferdinandi, Pure Fitness' regional fitness operations director. "However, the science no longer supported it.
"For training purposes, it is better to be able to train at near 100 per cent of the body's potential rather than place restrictions such as low oxygen that will inhibit positive adaptations," he says.
Intermittent hypoxic training (IHT) mask A slightly cheaper and more practical option, this is a hand-held mask to alternate short inhalations of hypoxic air, delivered from a hypoxicator, with inhalations of ambient air.
This reportedly triggers the desired adaptations in oxygen transport, improving aerobic and anaerobic performance.
The mask is available from Go2Altitude and Hypoxico. "With such training options, there is less chance to be overtrained. It helps to get me in peak physical condition before major games," says Asian Games medallist Daniel Lee Chi-wo, a former full-time triathlete at the Hong Kong Sports Institute. "But it has to be carefully monitored because it can have negative effects if not done properly."
Altitude house This is a full apartment where the oxygen pressure is reduced by flushing the premise with air diluted with nitrogen. The Hong Kong rowing team was based in such a house in Sweden while training at sea level.
"The effect of this training does not last a long time and will fade away quickly when the team comes back to sea level," says Perry. "It is really important to get the timing right before the competition."
Hypoxico offers the K2 high flow system for converting an apartment or office for high-altitude living, at HK$466,000.