We have learnt to enhance our strength centuries, millennia, ago first with lever then harvesting hydraulic and then steam power. Today we have a tremendous array of machines that multiply ur strength. Our body strength has also improved since our ancestors, we have grown taller (10 cm in average in the last 150 years) and the muscular mass has increased. It looks like, however, that this increase has levelled out and there are good physical and physiological reasons why we cannot get bigger and stronger.
Much more recently researchers have started to create exoskeletons, wearable machines that can diminish fatigue and multiply our strength. Whilst diminishing fatigue (including flanking no longer usable muscles as it is the case for exoskeletons for paralytic patients) is already being done, with an increasing level of effectiveness, the multiplication of strength carries problems that are of difficult solution in a general context whilst they already work well in limited context. The difficulty derives from the risk of hurting the person wearing the exoskeleton: imagine having to interact with a bulldozer not from the cockpit but from the moving blade and lift cylinder!
Military and health care are the two sectors steering the evolution.
We have drugs that can enhance our strength and decrease the sense of fatigue and a few people are using them. This goes along with dangerous side effects that make this approach quite risky. Besides, the present culture consider artificial improvement of strength a form of cheating (doping).
In the future we might expect to increase our knowledge on the effect of the genome on the phenotype also in relation to strength, hence there will be the possibility to make changes to the genotype to increase strength at the phenotype level.
It is, however, much more likely the the increase of strength will come from the evolution of exoskeletons. These, in certain applications, might become a seamless extension of our body. We have already taken the first step in this direction. Consider, as an example, skiing equipment. The boots can be designed on our foot shape, using 3d laser scan and 3d printing and can be made with smart material to absorb vibration and become more responsive.
Donning an exoskeleton at work might become as normal as using a screwdriver… BCI will also improve the capability of controlling robots to the point of having them becoming a seamless extension of our body and effectively multiplying our capabilities.
This will be another component in the evolution towards humans 2.0, transhumans.