Pack up your back troubles

My first rucksack looked as if someone had taken one of those shopping trollies beloved of women of a certain age, removed the wheels and attached a couple of straps to hold it on to my back. Not only was it an aesthetic nightmare, but anything more than two pairs of socks inside would cause the kind of muscular contortions sure to end up in backache even in a young man (as I was at the time).

Thank goodness things have moved on. Rucksacks may still look simple, but these days designers and engineers are carrying out extensive research to ensure that the final product is a far cry from a sack on straps.

The latest in backpacks, the Berghaus Bioflex C7 sac (winner of an award for outdoor product design at the Munich ISPO Expo), has been developed to provide a solution to the problems I experienced with my first backpack.

The work behind the Bioflex system was derived from military research undertaken by the Design Innovation Group at Qinetiq, to develop backpacks for soldiers in the field. The project involved looking at new concepts in load carriage and weight distribution for maximum efficiency (and comfort) and had built up a huge knowledge base that was only applied to field kit.

Qinetiq had considered some pretty extreme loading situations peculiar to military applications — fortunately not many ramblers are likely to need to carry a mortar over rough terrain — but the information gained by its Centre of Human Science was, nonetheless, extensive.

The potential for crossover to the retail sector was obvious and in 2003 Qinetiq contacted Berghaus as a possible partner to effect the transfer of the technology from the military to the commercial world.

By coincidence, Berghaus was also considering how to develop its backpack range to the next level, with a view to producing a next generation of ‘flexible’ backpacks designed to shape themselves to the person carrying them.

The original project had ground to a halt after a few years, largely because the company realised it need to devote a great deal more research and money to developing this ‘super backpack’.

Berghaus’s aim was to produce a new generation of backpacks that ‘could move ergonomically with the wearer, while still being able to lift up to 35kg on one strap, but weigh less than 2.5kg and retail at a maximum of £200’.

Lewis Grundy, Berghaus’s managing director, said, ‘We had given up on the project due to the development costs, but when Qinetiq   came to us and we secured 50 per cent funding for the project, to be repaid once the product turned in a profit, we were all for pushing it on as quickly as possible.’

The final design came about largely through empirical research. From its vast experience of backpacks the Berghaus team knew that the body is put under stress by the load shifting as the user walks. It also had to design a product with a high resistance to strain and abrasion damage that could be manufactured in volume.

The Qinetiq design work centred on the back system — the frame to which the bag and straps are attached. Chris Thorpe, capability leader for Qinetiq’s product design group, said: ‘We used our expertise to develop a flexible back system and worked with Berghaus over a number of years on the Bioflex. The end result has been a truly joint venture — it had to be to get the product to market within 18 months: our expertise in back systems helped greatly in this.’

The companies’ research identified a few reasons why we feel unstable when wearing a rucksack, one of which was the change in centre of gravity when a person straps on a heavy backpack. The natural human reaction is to lean forwards to compensate for this change of gravity. When the design team measured the effects of this leaning, it found that the average human spine expands by 8cm in a typical lean to adjust a backpack. This extension of the back leads to stresses if a pack is strapped on rigidly — a ‘splint effect’ that quickly causes fatigue.

The answer developed for the Bioflex is a lumbar pad, separate from the frame. This is secured to the shoulder section of the frame, and is free to move up and down as you lean forward, following the natural expansion of the spine. The rucksack is not all about simple two-dimensional spinal flexure mimicry, however.

The Bioflex system twists and pivots with the body as well — a feature that came after Qinetiq conducted extensive modelling of the complex twisting and flexing capabilities of our hip and lower back area. One of the big technical advances is the load transfer system developed by the team.

A rod made from Delrin, an inflexible, lightweight acetal polymer, is anchored in the hip section and arches over the top, transferring the load whichever way the body twists. It’s also important in keeping the weight distribution where it should be — studies indicated that around 70 per cent of a backpack’s weight is taken by the hips rather than the shoulders.

 As James Hodgson, equipment designer at Berghaus, put it: ‘Our design philosophy was based on freedom of movement with “positive load transfer”, a system we have developed in Bioflex.’

Once the outline of the flexible structure was decided, it was time to refine it into a product. To do this Berghaus built over 40 prototypes and put them through an exhaustive development and fine-tuning process.

Eighteen testers took pre-production models over hill and dale (as well as stiles and other awkward objects) for over 600 hours. After their feedback on how comfortable they found it, the team established the optimum positioning for all parts of the backpack.

Berghaus also built a number of test rigs to simulate the backpack’s interaction with the body — and tested their competitors’ products — to measure stresses and ensure that the new product is comfortable to wear.

The company now makes the bold claim of having the backpack that causes less stress on the body than any other on the market.