'Strength shoes,' special athletic shoes with four-centimetre (1.6-inch) hard-rubber platforms attached to the front halves of the soles, have become increasingly popular with athletes. The platforms are designed to elevate the feet and prevent the heels from striking the ground during activity. The idea is to make the calf muscles work like hell when you are carrying out your workouts

Being in the shoes is a bit like standing on a step with the edge of the step roughly in the middle of your feet and your heels hanging off the edge. 'To stay upright in the strength shoes, you've got to really activate your calf muscles; otherwise, you'll fall back on your butt,' says strength-training expert Walt Reynolds, C.S.C.S., Director of Personal Training at the Michigan Athletic Club.

You can run, bound, skip, jump, and do various plyometric drills while wearing the shoes, and all the time your calf muscles, including deep, often-neglected ones like the triceps surae, are working overtime. In the long run, such increased stress on the calves is supposed to build added power and - for runners - more explosive strides

To visualise how this happens, bear in mind that strength shoes are really designed to turn your feet into longer 'levers'. If you think about it, you'll realise that when you jump or run, your feet are actually levers acted upon mainly by the muscles in your calves. When you run, hop, or jump, those muscles pull up on your heels, rock you forward onto your toes, and send you forward. When you slip into the strength shoes, your feet are 'longer' because they now extend from your heels to the toes AND down to the ground through the strength shoes' platforms

As soon as a lever gets longer, more force must be applied at one end to make the opposite end move at its normal speed. This makes it easy to see what is supposed to happen when you strap on strength shoes. Since your 'levers' are now longer than normal, you must make your calf muscles contract with mega-force while you do your hops and plyometrics - just to move at normal speed. Otherwise, you'll look like a lumbering elephant as you move around the gym


But do they work?
Sounds good, but strength shoes hadn't actually been tested scientifically until recently, when scientists at Tulane University put the special shoes through some rigorous tests. Twelve intercollegiate track and field athletes, all participants in running or jumping events, followed a training regime recommended by the Strength Shoe manufacturers (Strength Footwear, Inc. of Metairie, Louisiana in the United States) over an eight-week time period. Half of the athletes wore their regular training shoes, while the other half attired themselves in strength shoes. The actual training regime consisted of stretching exercises and increasingly demanding plyometric drills. Workouts lasted about 45 minutes and were performed three times per week. In addition to this special regime, the athletes carried out their usual training

Unfortunately, the special strength shoes didn't do anything special. After eight weeks, ankle flexibility had improved by about the same amount - just 1 per cent - in both groups. Ankle strength was also about the same in the two groups, although there was a trend for the non-strength-shoe wearers to show stronger plantar flexion (ankle motion that occurs when the toes and top of the foot move away from - not toward - the shins)

Physical performance tests yielded much the same results. Strength-shoe and non-strength-shoe participants improved their 40-yard-dash times by about the same amount. Improvement in vertical leaping ability was actually slightly greater in the non-strength-shoe people, although the difference wasn't statistically significant. Calf size was also nearly identical between the two groups (although not a key indicator of performance potential, calf size was measured by the researchers because the Strength Shoe manufacturers claimed that the devices would boost calf diameter)


The danger of pain
Disturbingly, two of the six subjects wearing strength shoes developed anterior tibial ('shin-splint') pain during the training period, and one of these athletes actually had to leave the study after four weeks because the pain was so intense. Neither of the two athletes had experienced leg pain before the research began, and none of the people who trained in regular shoes encountered lower-limb discomfort during the research. As the Tulane investigators put it, 'This is strong circumstantial evidence to indicate a relationship between the use of the strength shoe and anterior tibial pain'

So what conclusions should we draw about strength shoes? Theoretically, training with the shoes doesn't seem to be such a bad idea. After all, our muscles and tendons behave a lot like springs. If you stretch springs, they contract forcefully. If you stretch them even more, they contract even more forcefully. Strength shoes are designed to enhance this stretching of the calf muscles and tendons, force the calf muscles to exert more power during exercise, and therefore make the calves more powerful over time. For runners, that should produce quicker, longer strides

The problem is, plyometric training with strength shoes doesn't seem to work any better than plyometric training in regular shoes, at least over an eight-week time period. Why aren't the strength shoes effective? One reason may be that a major portion of the benefits which accrue from plyometric training may result from improved proprioception, eg, an enhanced ability to respond to changes in body position and the physical tension of muscles while you are engaged in your sport. Wearing strength shoes would upgrade proprioception while wearing the special shoes - but not necessarily while wearing normal shoes. Of course, normal shoes are the ones used for very strenuous regular training, performance tests, and competitive situations

Unfortunately, the use of strength shoes was also associated with a high risk of injury, at least in the small group of Tulane athletes. Based on this shin-pain problem and the lack of scientifically verified benefits associated with strength-shoe training, we cannot recommend the use of strength shoes. Plyometric training is valuable for athletes, but there's at present no reason to carry out the training while attired in strength shoes.

('Development of Lower Leg Strength and Flexibility with the Strength Shoe,' The American Journal of Sports Medicine, vol. 21 (3), pp. 445-448, 1993)
Gordon Quick

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