ECR Spotlight – Benjamin Sibson Free

Benjamin Sibson

How did you become interested in biology?

Growing up just south of Adirondack Park in upstate New York, USA, I was lucky to have parents who encouraged me to be outside often. I enjoyed watching bluebirds fly, oak trees shake in the wind, deer forage and other natural phenomena. Being an active kid, whether walking, running, biking or skiing, I also appreciated the joy of movement. All this time in nature gravitated me towards biology in high school, but I think suffering a few broken bones really got me considering biology as a potential career. Between ages 14 and 17 I broke both wrists, my left collarbone, my left ankle and had a stress fracture in my left patella, all from playing various sports. In recovering from these injuries, I recognized what a privilege movement is and became more aware of the structure and function of my muscles, bones and ligaments. These experiences coalesced into a decision to pursue an undergraduate degree in a biological science, namely Kinesiology and Applied Physiology at the University of Delaware, USA, followed by a PhD in Human Evolutionary Biology at Harvard University, USA.

Describe your scientific journey and your current research focus

I got involved in research in my freshman year at the University of Delaware, when my Intro to Exercise Science professor Christoper Knight kindly invited me to help collect and analyze data in his Exercise Neuroscience Lab. We studied the effect of high-intensity cycling training on physical function in people with Parkinson's disease, and I ended up writing a Senior Thesis on this work. In one lecture of that Intro to Exercise Science course, I was first introduced to the study of physical activity from an evolutionary perspective. Fascinated by the idea of integrating exercise science with human evolution to try to understand why physical activity can be beneficial to health, I applied to do my PhD in Dan Lieberman's Skeletal Biology and Biomechanics Lab at Harvard University. My doctoral dissertation tested the effect of variation in physical activity on trunk muscle endurance and lumbar spine function and was a combination of lab-based experiments in the USA and field-based experiments with subsistence farmers in Kenya and Rwanda. The main takeaway from my PhD work is that being physically active seems to help develop endurance of back muscles, which itself impacts trunk neuromuscular control during walking. As a postdoc in Dennis Anderson's lab, my current research expands upon my PhD work to investigate how training to improve trunk neuromuscular control affects spine biomechanics during gait in older adults with and without low back pain. Overall, these steps of my scientific journey have merged to a research focus of studying the biomechanics of human movement from an evolutionary perspective and its relevance to health and disease.

How would you explain the main findings of your paper to a member of the public?

The main finding of this paper is that the endurance of back muscles affects how the lumbar spine functions during walking. In this context, endurance refers to the capacity of muscle to resist fatigue and keep generating force (which is how muscles pull on bones to make humans and other animals move). When we fatigued participants' backs with an exercise test and then asked them to walk on a treadmill, those who had less back muscle endurance to begin with increased the activity of their abdominal muscles and decreased the activity of their back muscles. We also observed that individuals with less back muscle endurance began loading their lumbar spines – the lowest part of the spine, between the mid-back and waistline – more. To our surprise, those who had higher back muscle endurance to begin with showed an opposite response: they decreased abdominal muscle activity and increased back muscle activity while walking. Our take-home message is that depending on a person's back muscle endurance, their nervous system and muscles seem to function differently while they are walking when their back is fatigued. There's good evidence to suggest that having back muscles with more endurance may prevent back pain. Maybe part of the reason why is that – since everybody experiences having a tired back at some point – having higher back muscle endurance helps the lumbar spine continue to function properly while walking.

What is the most important piece of equipment for your research, what does it do and what question did it help you address?

The most important piece of equipment for my research is computer-based musculoskeletal modeling. A key question biomechanics tries to address is the relationship between a biological structure's form and its function, and oftentimes an important piece of this equation are the forces acting on the structure. For example, I might be interested in relating the compression force acting at the lumbosacral joint (the most inferior intervertebral joint, between the lumbar spine and sacrum) to the morphology of the L5 vertebra. However, there's a significant problem: without something like a force transducer implanted in the L5 vertebra – which is prohibitively invasive, hence effectively impossible for experimental work – there is no feasible way to directly measure joint forces. The best alternative is to estimate these forces using musculoskeletal models. By measuring kinematics using motion capture, ground reaction forces using force plates, and basic anthropometrics such as height and body mass, it is possible to derive and solve equations of motion for body segments and joints to calculate accurate estimates of joint moments and forces. Computer-based models solve these equations automatically in a fraction of the time it would take to do so by hand. Moreover, more advanced models, such as in the opensource software OpenSim, can go even further, using algorithms such as static optimization to generate estimates of the individual muscle forces that must have been acting to cause an observed motion. Computer-based musculoskeletal modeling helps biomechanists answer questions about the relationship between a biological structure's form and its function.

What is your favourite animal, and why?

My favorite terrestrial animal is the white-handed gibbon (Hylobates lar). Considered one of the ‘lesser’ apes (as opposed to ‘great’ apes like mountain gorillas and bonobos), white-handed gibbons are located in southeast Asia and are severely threatened by habitat destruction and hunting. They are my favorite animal because of how they most commonly move: white-handed gibbons use a form of arboreal locomotion called brachiation, which involves arm swinging beneath branches from tree to tree. Brachiation is such an athletic way of moving, and white-handed gibbons are marvelously adapted to this form of locomotion with their long arms and short, compact lumbar spines. My favorite marine animal is the blue whale (Balaenoptera musculus), the largest animal ever known to have existed on Earth. I'm particularly a fan of how long their seasonal migrations are. Blue whale migrations can be over a thousand miles in each direction, and it's fascinating to consider an animal traveling over such a long distance over such a long time, powered by its flukes, flippers and helpful ocean currents.