The huge muscles sculpted by bodybuilders, action movie stars and serious gym-goers can make them look like comic-book superheroes. And we tend to equate big muscles with being strong and powerful.
But new research has found that - at a cellular level - the large, defined muscles seen on bodybuilders don't fare well against those of power athletes (such as weight lifters or sprinters) or even men who don't train at all.
The research, published in Experimental Physiology, was carried out on individual muscle cells taken from a group of volunteers comprising 12 bodybuilders, six power athletes and 14 control subjects (average men, physically active but not doing weight training).
The researchers, led by Hans Degens of Manchester Metropolitan University, stimulated the cells and assessed the size and speed of the force produced from the resulting isometric contractions (contracting while staying the same length). By measuring the size of the muscle cell, they were able to calculate what is known as the specific force, the force produced for a defined area or unit of muscle. The higher the specific force, the better quality the muscle.
The study found that although the individual fibres of the bodybuilders' muscle cells were considerably larger than those of the control group, they also had a lower specific force. This suggests that their muscles were of a poorer quality than those of the controls. The power athletes, who also used resistance training but lifted lighter weights more quickly, had similar quality muscles to the controls but were able to produce the force more quickly, meaning their muscles were more powerful.
These findings need to be put in context. Our skeletal muscle fibres function as part of a wider body system. Weightlifting can increase the size of skeletal muscles but it can also improve the function of supporting connective tissues and blood vessels and engage the nervous system to use more of the available muscle.
This means a lower specific force at a microscopic level does not necessarily equal a poorer quality muscle or impaired function at a whole body level. As such, we shouldn't be surprised that former bodybuilders have been able to dominate strength competitions while retaining much of their bulk.
Physiologists have known for decades that a strong but imperfect and complex relationship exists between the size of a muscle and the force it can produce. Generally, the bigger the muscle, the more force it can produce. However, some studies have noted that larger muscles do not have an equivalently large improvement in the specific force.
This means as the muscle gets bigger there is not an equal increase in muscle quality. This is thought to be due to changes in muscle architecture or to a dilution of the proteins that do the work of muscle contraction. Similar results occur when muscle size is enhanced with anabolic steroids or testosterone.
It seems like there is an optimal size for a muscle, above which increases in size do not necessarily lead to the same relative improvements in strength.
The situation is different for power athletes, who train with weights in a very different way to bodybuilders. While bodybuilders train to grow their muscles to their genetic potential with the help of diet and sometimes drugs, power athletes try to maximise their strength at a specific body weight. The differences in training strategies combined with a constant need to maintain weight within a given category probably prevent the power athletes from growing their muscles to the sizes seen in bodybuilders.
In a great example of the strength differences, former world record holder for the squat, Fred Hatfield, was able to lift over 90kg more than bodybuilder Tom Platz in a competitive "squat-off", despite having visually much less impressive legs.
Such anecdotal reports show that when it comes to a muscle's response to weight lifting, size might not be everything.
Lee Hamilton lectures in sports science, and Angus Hunter exercise physiology, at the University of Stirling.