Colin Griffin, The Altitude Centre Ireland  
When an athlete or player is side-lined as a result of injury, it can be a very frustrating experience. It can be a costly one too for professional athletes, as missing a competition due to injury can result in loss in earnings where prize money or match bonuses are involved. The prolonged time that an athlete spends unable to train can have physical as well a psychological consequences. Loss of competitive fitness and physical condition can result from a period of inactivity. Regaining that match or race fitness following a period of inactivity can be further time-consuming. There is also the psychological effect of not being able to train or compete while teammates and rivals can, which can affect an athlete’s confidence and morale.
Hypoxic training can benefit an injured athlete or player in the rehabilitation process in the following ways:
·       Accelerate healing and recovery from injury, and return to full training and competition sooner
·       Maintaining fitness whilst injured
·       Avoid unwanted weight gain whilst injured
Accelerate injury recovery time
Cells and tissue require oxygen for survival and function. When there is an injury to tissue or bone, oxygen is required for healing. When cells and tissues are in a hypoxic state a number of adaptive responses occur as they make better use of the limited oxygen available.  In fact when an injury is sustained, the injury site itself becomes hypoxic due to the vascular disruption secondary to the injury. This hypoxic microenvironment acts as a protective mechanism for recovery by stimulating the expression of a variety of repair proteins, fibroblasts, endothelial cells and osteoblasts, whilst the tissue inhibitor of metalloproteinase-1 is decreased.
There are many reported therapeutic benefits of hypoxic training for healing and recovery of both soft tissue and bone injuries. Hypoxic exposure increases capillarization, which in turn increases blood flow and oxygen delivery to the site of injury. Mitochondrial density and efficiency is also increased at cellular level. There have been some studies which indicate that intermittent hypoxic exposure can be used in the treatment of spinal cord injuries, as hypoxia is said to stimulate nerve growth with augmented crossed spinal synaptic pathways (Golder et al 2005). Human Growth Hormone secretion can be increased by up to 215% following as little as 10 minutes hypoxic exposure (Davydov et al 2001). Growth hormone is vital for injury repair as it stimulates tissue and skeletal growth.
There is some suggestion that hypoxia can positively influence stem cell migration to the injury site to enhance tissue regeneration. Stem cells live in the bone marrow which is an already hypoxic environment with a mean oxygen saturation of 87.5% (Harrison et al 2002). It could be argued that peripheral hypoxia could create the right conditions to aid stem cell migration to the injury site by replicating the same hypoxic conditions that exist in the bone marrow. Hypoxic pre-conditioning of stem cells prior to a bone marrow transplant is something that is being explored in the medical field.
In the case of bone injuries such as a fracture, there are anecdotal reports by sports doctors that suggest quicker bone healing time by utilising hypoxic training during rehabilitation. Hypoxia can improve bone healing by altering the expression of cytokines, extracellular matrix scaffolding molecules (collagens I and III), and their regulators (Warren et al. 2001). Athletes who suffer stress fractures or a full fracture have used Intermittent Hypoxic Exposure (IHE) as part of their injury rehabilitation with some positive results. Some athletes have often used supplementary oxygen therapy such as a hyperbaric chamber to assist with bone healing. A daily course of IHE for a period of time can trigger the body’s own adaptive response to deliver extra oxygen to the injury site and accelerate healing.
Intermittent Hypoxic Exposure (IHE), which involves short bursts of oxygen reduced air using a mask and hypoxic generator, followed by equal bursts of room air; is a very effective hypoxic training technique for injury rehabilitation and one endorsed by many leading physiotherapists. During acute bouts of hypoxic exposure, blood shifts from the periphery to the core to protect the vital organs with increased blood flow. This shift in blood flow can have a similar effect as applying ice or using cryotherapy as the same vasoconstrictions occur. The peripheral cells become more receptive to oxygen as they scavenge the limited supply available. When normal oxygen supply has resumed, vasodilation occurs and blood supply is restored. Greater oxygen is delivered to the peripheral cells whilst they are in their most receptive state.
It must be said however, that further research is required in this area. But there is some evidence and potential to suggest that hypoxic training can be a useful aid the healing of soft tissue and bone injuries.
Maintain fitness levels while injured
As outlined in Part 1, training in a hypoxic environment places a greater cardio-respiratory challenge on the body, which triggers a host of physiological and muscular adaptations. Training in hypoxia makes any given workload more challenging than in normal room oxygen conditions (normoxia).
An athlete or player with an acute or chronic injury requires a carefully prescribed injury management and rehabilitation program.  Maintaining cardiovascular fitness without aggravating the injury site is desirable.  In most cases this can be achieved by cycling on a stationary bike or using a cross-trainer. With the addition of a hypoxic generator and exercise mask system, or indeed a hypoxic chamber, the athlete can do these cross-training sessions at simulated altitude and therefore achieve a greater cardiovascular stimulus. Such is the quality of the workout, that some coaches have reported field sport players returning from injury recording personal best times in fitness tests following a period of cross-training using hypoxic training.
The use of Alter-G anti-gravity treadmills has become a widespread and popular injury rehabilitation tool. By exercising at a reduced body weight, the athlete or player can train at a high neuromuscular intensity and volume without fully loading the body. However due to the reduced gravity at which the athlete or player is exercising, it can be difficult to achieve the heart rate elevations required to achieve sufficient cardiovascular stimulus. By having an Alter-G treadmill in a hypoxic chamber or using a hypoxic exercise mask system with it, a high cardiovascular load can be achieved while exercising at reduced weight bearing load. In more extreme cases where an athlete is completely immobilised in the lower limbs (e.g. a bone fracture or ACL injury), they can do seated training sessions using a hand bike or boxing bag and achieve a challenging upper body workout with an intense cardiovascular stress in hypoxia.
Hypoxic training can also be beneficial for athletes who are older or more injury prone and require careful management of training load and extra recovery between physical workouts, particularly in field sports. Implementing hypoxic sessions into the training program in place of some field sessions, can ensure that a good cardiovascular stimulus is achieved without the physical strain and impact on the body. The same would apply to fatigued players. Players who are deconditioned can benefit from hypoxic training to accelerate their return to match fitness without having to overload themselves on the pitch.
Athletes can maximise their injury rehabilitation by working at a higher intensity and at a reduced volume load in hypoxia compared to sea-level sessions, therefore getting a greater ‘bang for their buck’. They can maintain their confidence and morale by feeling that they are doing something positive and constructive during their injury recovery period. However, like any injury rehabilitation programme, we strongly advise close medical supervision throughout with their physiotherapist or sports medicine doctor.
Avoid weight gain while injured
When an athlete is injured and unable to train at full capacity for a period of time, they often find that their weight increases due to decreased calorie expenditure. When an injured athlete uses hypoxic training methods and assuming they control their calorie intake, they will find that they will at least maintain if not reduce their body weight due to the increased metabolism under hypoxic conditions. Even low intensity physical exercise three times per week for 90 min in normobaric hypoxia for 8 weeks led to significantly greater weight loss in obese persons compared to the same work in normoxia (Netzer et al 2008)
Hypoxic exposure increases the body’s metabolism with increased carbohydrate utilization and glycolysis due to the regulatory role played by the Hypoxia Inducible Factor 1 alpha (HIF1-α) gene. As a result, under these hypoxic conditions; cells adapt metabolically from aerobic to anaerobic metabolism in order to generate ATP in an oxygen-independent manner. The HIF1-α gene triggers a shift from fat to carbohydrate as the primary fuel source in hypoxia. Because carbohydrates have a higher yield of ATP per mole of oxygen, greater use of muscle glycogen and blood glucose occurs. Fat catabolism increases under hypoxic conditions if carbohydrate supply is inadequate. Loss of muscle mass can occur also, therefore adequate intake of protein and essential BCAA’s is recommended to preserve muscle mass. Hypoxic exposure at rest (Live High Train Low using altitude tent, or Intermittent Hypoxic Exposure) will increase basal metabolism. High intensity hypoxic training will increase exercise metabolism as well as basal metabolism for several hours after a training session.

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