The general volume of air traffic has risen greatly in recent years and an important component of this is the increase in the number of long-haul flights. According to International Civil Aviation the annual number of flight passengers exceeded 1647 million in 2006 and that number is expected to rise by 4.4 per cent each year by 2015 (World Health Organization, 2007). Contemporary aircraft can cover longer distances without the need for stop-over, thus prolonging the duration of the flight. Moreover, in order to fit more passengers on the economy class flights, the airline industry tends to put additional seats in the cabin. This reduces the already insufficient legroom space even further, consequently increasing passengers’ immobility.
The altered and restricted environment in an air-craft cabin, carries possible health risks for people aboard. One such flight-related danger is the development of a deep vein thrombosis (DVT) in the lower legs, which can lead to potentially fatal conditions, particularly pulmonary embolism (PE). DVT relates to a condition caused by the formation of a blood clot (i.e. thrombus) in deep veins usually of the legs. When such blood clot breaks off it can travel through the veins back to the heart, and eventually be pumped by the heart into the lungs causing a blockage leading to the potentially fatal condition called pulmonary embolism.
Venous thromboembolism (VTE – both DVTs and PEs) after long-haul flight was first reported more than 50 years ago (1954). Since then multiple case reports and epidemiological studies provided further evidence of an association. VTE have been connected with at least 577 deaths on 42 of 120 airlines from 1977 to 1984 (25 deaths/million departures), although a proportion of such cases go unreported (Greenleaf, et al. 2004) primarily due to the fact that majority of DVT are asymptomatic and resolve spontaneously or occur days after the flight. It is crucial to acknowledge the fact that VTE is not unique to air travel but it is a complication also associated with other modes of transport, or rather any form of prolonged immobility.
It remains unclear whether the aircraft-specific factors, such as hypobaric hypoxic conditions and lower humidity, create an increased risk compared with seated immobility at ground level. There is very little evidence for the direct causative relationship between air travel and DVT in the healthy flying population. In fact the major danger is for those people who fly with multiple risk factors for DVT. For example, mutation in certain genes responsible for increased blood coagulability, history of VTE, venous insufficiency, obesity, and infectious diseases, to name a few.
Nevertheless, various preventive treatments and techniques have been proposed as countermeasures for possible flight-induced DVT. One such procedure is exercise of the lower extremities, especially the calf (soleus and gastrocnemius) muscles, in order to increase intracapillary pressure facilitating venous flow thus preventing blood from clotting (Paganin, 2003).
What is less clear is the appropriate frequency, duration and intensity of exercise in different environments and different populations. Identification of this will help to minimise risks during travel. Here at LSBU we are currently carrying out experiments that are attempting to answer these questions.
Saturday 16 February 2008
Friday 15 February 2008
Step-to-step transitions are mechanically different during walking.
Step-to-step transitions are mechanically different during walking.
Darren James
Sport & Exercise Research Centre, London South Bank University.
Ever wondered how we walk? The answer for the majority of us is probably not. But it was the asking of this question that led to the development of FitFlopTM, which was designed as a training aid to increase the metabolic cost of walking.
Generally, it is not until the ability to walk is taken away such as during injury and in disease do we realise what we have lost. Our gait pattern is as unique and individual as our DNA, yet while each step appears on the surface to be repeatable this cannot be said for the internal mechanics that govern this motion.
Take for example the below illustration, which clearly shows how quadriceps (m. vasti medialis) muscle activity alters with each step during undisturbed barefoot walking. The top half of the diagram consists of the power from each step resulting from accelerations recorded at the lower leg of a 59kg female subject aged 19. Dr. Joseph Hamill and colleagues at the University of Massachusetts, USA, have previously used this method of analysis in a 1995 study. Each graph produces two distinct peaks which relate to the power resulting from active movement and a higher frequency peak associated with energy due to ground impact.
The first graph (from left to right) is the initiation step which shows low power in both peaks due to a lack of momentum. In the next step, the power of active movement is twice that of impact, and shows greater muscle activity than the initiation step. Is this too much central control? Obviously so, as the next step shows reduced active movement power but greater power of the ground impact peak suggesting a greater reliance on an eccentric contraction of the knee extensor muscle to effectively damp the resulting shock transmission. Consequently, because of this, the system is tuned for the next step (last graph – far right) with the greatest recorded active movement power and muscle activity, and reduced impact power.
So what? Well this clearly describes the energetics of walking by highlighting that the magnitude of low frequency power from ground impact is a result of alterations in muscle activity. This understanding is beneficial in the design of footwear for healthy people, clinical interventions or as training tools.
If we can show that manipulations in footwear increase lower extremity muscle activity, such as FitFlopTM; then the exercise ratio of return (ROR) may well exceed that of other fitness activities in providing an effective workout by simply wearing a form shoe.
So by safely perturbing your gait pattern it is possible to increase the metabolic cost of walking and increase the training benefits of low impact activities such as walking.
Darren James
Sport & Exercise Research Centre, London South Bank University.
Ever wondered how we walk? The answer for the majority of us is probably not. But it was the asking of this question that led to the development of FitFlopTM, which was designed as a training aid to increase the metabolic cost of walking.
Generally, it is not until the ability to walk is taken away such as during injury and in disease do we realise what we have lost. Our gait pattern is as unique and individual as our DNA, yet while each step appears on the surface to be repeatable this cannot be said for the internal mechanics that govern this motion.
Take for example the below illustration, which clearly shows how quadriceps (m. vasti medialis) muscle activity alters with each step during undisturbed barefoot walking. The top half of the diagram consists of the power from each step resulting from accelerations recorded at the lower leg of a 59kg female subject aged 19. Dr. Joseph Hamill and colleagues at the University of Massachusetts, USA, have previously used this method of analysis in a 1995 study. Each graph produces two distinct peaks which relate to the power resulting from active movement and a higher frequency peak associated with energy due to ground impact.
The first graph (from left to right) is the initiation step which shows low power in both peaks due to a lack of momentum. In the next step, the power of active movement is twice that of impact, and shows greater muscle activity than the initiation step. Is this too much central control? Obviously so, as the next step shows reduced active movement power but greater power of the ground impact peak suggesting a greater reliance on an eccentric contraction of the knee extensor muscle to effectively damp the resulting shock transmission. Consequently, because of this, the system is tuned for the next step (last graph – far right) with the greatest recorded active movement power and muscle activity, and reduced impact power.
So what? Well this clearly describes the energetics of walking by highlighting that the magnitude of low frequency power from ground impact is a result of alterations in muscle activity. This understanding is beneficial in the design of footwear for healthy people, clinical interventions or as training tools.
If we can show that manipulations in footwear increase lower extremity muscle activity, such as FitFlopTM; then the exercise ratio of return (ROR) may well exceed that of other fitness activities in providing an effective workout by simply wearing a form shoe.
So by safely perturbing your gait pattern it is possible to increase the metabolic cost of walking and increase the training benefits of low impact activities such as walking.
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