Unfortunately, soft tissue does not fossilize (which is a problem for facial reconstructions of hominins; Stephan and Henneberg, 2001; I will cover the recent ‘reconstructions’ of Neanderthals and Nariokotome boy soon). So saying that Neanderthals had X percent of Y fiber type is only conjecture. However, to make inferences on who was stronger, I do not need such data. I only need to look at the morphology of the Neanderthals and Homo sapiens, and from there, inferences can be made as to who was stronger. I will argue that Neanderthals were stronger which is, of course, backed by solid data.
Neanderthals had wider pelves than Homo sapiens. Wider pelves in colder climes are due to adaptations. Although Neanderthals had wider pelves than ours, they had infants around the same size as Homo sapiens, which implies that Neanderthals had the same obstetric difficulties that we do. Neanderthals also had a pelvis that was similar to Heidelbergensis, however, most of the pelvic differences Neanderthals had that were thought to be derived traits are, in fact, ancestral traits—except for the cross-sectional shape of the pubic ramus (Gruss and Schmidt, 2015). Since Neanderthals had wider pelves and most of their pelvis were ancestral traits, then wide pelves may have been a trait of ancestral Homo (Trinkaus, Holliday, and Aurbach, 2014).
Hominins do need wider pelves in colder climates, as it is good for heat retention, however (see East Asians and Northern Europeans). Also, keep in mind that Neanderthals were shorter than us—with the men averaging around 5 feet five inches, and the women averaging about 5 feet, about 5.1 inches shorter than post-WW II Europeans (Helmuth, 1998).
So what does a wider pelvis mean? Since the Neanderthals were shorter than us and also had a wider pelvis, they had a lower center of gravity in comparison to us. Homo sapiens who came Out of Africa, had a narrower pelvis since narrow pelves are better to dissipate heat (Gruss and Schmidt, 2015). Homo sapiens would have been better adapted to endurance running and athleticism, in comparison to the wide-pelved Neanderthals.
People from tropical climates have longer limbs, and are tall and narrow (which is also good for endurance running/sprinting) while people from colder climates are shorter and more ‘compact’ (Lieberman, 2015: 113-114) with a wide pelvis for heat retention (Gruss and Schmidt, 2015). So, clearly, due to the differences in pelvic anatomy between Homo sapiens and Neanderthals,
Furthermore, due to the length of Neanderthal clavicles, it was thought that they had long clavicles which would have impeded strength. However, when the clavicles were reanalyzed it was discovered that when the clavicles were adjusted with the body size of Neanderthals—and not compared with the humeral lengths—Neanderthals had a similar clavicular length, which implies a similar shoulder breadth as well, to Homo sapiens (Trinkaus, Holliday, and Aurbach, 2014). This is another clue that Neanderthals were stronger.
Yet more evidence comes from comparing the bone density of Neanderthal bones to that of Homo sapiens. Denser bones would imply that the body would be able to handle a heavier load, and thusly generate more power. In adolescent humans, muscle power predicts bone strength (Janz et al, 2016). So if the same holds true for Neanderthals—and I don’t see why not—then Neanderthals would have higher muscle power since it predicts bone strength.
Given the “heavy musculature” of Neanderthals, along with high bone robusticity, then they must have had denser bones than Homo sapiens (Friedlander and Jordan, 1994). So since Neanderthals had denser bones, then they had higher muscle power; they had a lower center of gravity due to having a wider pelvis and being shorter than Homo sapiens whose body was heat-adapted. Putting this all together, the picture is now becoming clearer that Neanderthals were, in fact, way stronger than Homo sapiens.
Another cause for these anatomical differences between Neanderthals and Homo sapiens is completely independent of cold weather. Neanderthals had an enlarged thorax (rib cage), which evolved to hold an enlarged liver, which is responsible for metabolizing large amounts of protein. Since protein has the highest thermic effect of food (TEF), then they would have had a higher metabolism due to a higher protein diet which would also have resulted in an enlarged bladder and kidneys which are necessary to remove urea, which possibly would have also contributed to a wider pelvis for Neanderthals (Ben-Dor, Gopher, and Barkai, 2016).
During glacial winters, Neanderthals would have consumed 74-85 percent of their calories from fat, with the rest coming from protein (Ben-Dor, Gopher, and Barkai, 2016). Neanderthals also consumed around 3,360-4,480 kcal per day (Steegman, Cerny, and Holliday, 2002). Let’s assume that Neanderthals averaged 3800 kcal per day. Since the upper limit of protein intake is 3.9 g/bw/day (erectus) and 4.0 g/bw/day for Homo sapiens (Ben-Dor et al, 2011), then Neanderthals would have had a theoretical higher upper limit due to having larger organs, which are useful in processing large amounts of protein. The protein intake for a Neanderthal male was between estimated to be between 985 kcal (low end) to 1170 kcal (high end). It was estimated that Neanderthal males had a protein intake of about 292 grams per day, or 1,170 kcal (Ben-Dor, Gopher, and Holliday, 2016: 370).
Assuming that Neanderthals did not eat carbohydrates during glacial winters (and even if a small amount were eaten, the model would not be affected) and an upper limit of protein intake of 300 grams per day for Neanderthal males, this implies that 74-85 percent of their diet came from animal fat—the rest being protein. Protein is the most thermogenic macro (Corvelli et al, 1997; Eisenstein et al, 2002; Buchholz and Schoeller, 2004; Halton and Hu, 2004; Gillingham et al, 2007; Binns, Grey, and Di Brezzo, 2014). So since Neanderthals ate a large amount of protein, along with their daily activities, they had to have had a high metabolic rate.
To put into perspective how much protein Neanderthals ate, the average American man eats about 100 grams of protein per day. In an analysis of the protein intake of Americans from 2003-2004, it was found that young children ate about 56 grams of protein per day, adults aged 19-30 ate about 91 grams of protein per day, and the elderly ate about 56 grams of protein per day (Fulgoni, 2008). Neanderthals ate about 3 times the amount of protein than we do, which would lead to organ enlargement since larger organs are needed to metabolize said protein as well. Another factor in the increase of metabolism for Neanderthals was the fact that it was, largely, extremely cold. Shivering increases metabolism (Tikuisis, Bell, and Jacobs, 1985; van Ooijen et al, 2005). So the Neanderthal metabolism would have been revved up close to a theoretical maximum capacity.
The high protein intake of Neanderthals is important because high amounts of protein are needed to build muscle. Neanderthals consumed a sufficient amount of kcal, along with 300 grams of protein per day on average for a Neanderthal male, which would have given Neanderthals yet another strength advantage.
I am also assuming that Neanderthals had slow twitch muscle fibers since they have wider pelves, along with evolving in higher latitudes (see Kenyans, East Asians, European muscle fiber distribution), they would have an abundance of type slow twitch muscle fibers, in comparison to fast twitch muscle fibers, however, they also have more slow twitch fibers which Europeans have, while African-Americans (West-African descendants) have a higher amount of fast twitch fibers. (Caesar and Henry, 2015). So now, thinking of everything I explained above and replacing Neanderthals with Europeans and Homo sapiens with Africans, who do you think would be stronger? Clearly, Europeans, which is what I have argued for extensively. African morphology (tall, lanky, high limb ratio) is not conducive to strength; whereas European morphology (wide pelvis, low limb ratio, an abundance of slow twitch fibers) is.
The implications for these anatomic differences between Neanderthals and Homo sapiens and how it translates into racial differences will be explored more in the future. This was just to lay the anatomic and morphologic groundwork in regards to strength and cold weather adaptations. Nevertheless, the evidence that Neanderthals were stronger/more powerful than Europeans stands on solid ground, and the same does hold for the differences in strength between Africans and Europeans. The evolution of racial pelvic variation is extremely important to understand if you want to understand racial differences in sports.