Biomechanics for Tree Climbers

This story starts as many stories do, with a life-changing incident. But it is really about body mechanics.

In 2007, I (Phil Kelley) had a lead fail under me while doing a large crane removal. I was at the end of the lowest limb of a 66-inch DBH (diameter-at-breast-height) water oak, so when the lead failed, I swung through the air a long way before striking the trunk with the right side of my body. This caused injury to my shoulder and ribs, but really destroyed my elbow.

I had 27 fractures in the radial bone of my right arm (Photos 1&2). They put a plate and multiple screws in my arm to try and hold everything together. After six months of physical therapy, I returned to climbing. Within three months, the pain was unbearable. Due to all the metal in my arm and the location of the pain, they couldn’t see what was going on, so they had to do another surgery to investigate.

Photo 1: X-ray of the arm with the screws in.
X-ray images courtesy of Phillip Kelley.

It turns out that, due to all the missing bone fragments, the plate in my arm had shifted and was scraping on the humerus bone of the upper arm. The only solution was to remove the plate, screws and all the bone pieces of the radial bone in my arm. They also removed the damaged part of the humerus and the inside of the elbow bone. Due to this, I was told I would never climb trees again. As a matter of fact, I was told I would not be able to lift more than 30 pounds with my right arm.

Photo 2: X-ray with the radial head removed.

This prognosis was devastating – the only thing I had done since I was 17 years old was climb trees. It wasn’t just what I did, it was who I was. My entire identity was tied to tree climbing. I was lost and scared. I had three daughters to take care of, and my only source of income was what I was told I could no longer do. The only solution was to figure out a way to continue to climb, and to do this I had to look at the mechanics of how we climb and adapt to my limitations, if possible.

When I left physical therapy, my grip strength in my left arm was 110 pounds, but it was only 30 pounds in my right. So I needed to figure out how to climb without using my right arm as the sole source of strength and movement of rope. This led me to partner with Odis Sisk, a fellow climber, to do some research on grip strength and how we, as climbers, use our arms during an average day. We also looked at the tools we were using to see if there were ways to modify the tools or the way we use them to make climbing easier.

We began with the research on grip strength, as that was the most noticeable area of strength loss and limitation to climbing. Here is what we found testing on arborist lines of varying diameter:

• 50 mm (2-inch) line – Best grip strength, but muscle strength deteriorates most rapidly with work cycles.

• 38 mm (1.5-inch) line – Maximum number of work cycles before fatigue.

• 31-38 mm (1.22- to 1.5-inch) line – Least reduction in grip strength through repeated cycles.

• 22 mm (.86-inch) line – Best for manipulation.

• 8-16 mm, optimal 12 mm (.5-inch) line – Best for precision grip.

Based on this research, the smaller-diameter arborist ropes are not the most optimal for grip strength or time under tension. Using this data, we decided to test arborists to see where they fell with regard to grip strength and shoulder mobility, and the results were very interesting.

We know that handgrip strength of:

• 123 to 141 pounds is excellent;

• 114 to 122 pounds is above average;

• 105 to 113 pounds is average; and

• 96 to 104 pounds is below average.

We tested 30 climbers at two different climbing competitions. Their average years of climbing was 16, and the average weight of the climbers was 176 pounds. We tested with a hand dynamometer with the arm extended and again with the elbow bent. We found that, with the arm extended, the left arm average strength was 88 pounds and the right arm was 89 pounds. With elbow bent, we found the left hand was 95 pounds and the right hand was 102 pounds. So, as a group, tree climbers are right-hand dominant and are below average in grip strength.

This was the opposite of what I thought we would find, which was that, because of us doing all the climbing and pulling we do, we would be stronger. I attribute the low numbers to fatigue and overuse. I wonder if the numbers would be higher if we gave participants a week’s vacation before testing. I also wonder if there is a correlation between time under tension and fatigue. Is this a permanent condition? Can we mitigate some of this by increasing the diameter of the ropes we use?

I have found significant improvements in my ability to climb with my arms when using a half-inch climbing line. The other game changer has been the use of tactile gloves.

This research led to more questions, and I was fortunate enough to meet Alexander Levar and learn about the research he has been doing with biomechanics and how some small changes in climbing techniques can extend our climbing careers. I’ll let Alex take it from here.

Optimized techniques for tree climbers

In 2018, Fund4Trees, the Arboricultural Association (United Kingdom), TREE Fund and Teufelberger announced funding for a project intending to map the body’s movements during tree climbing, utilizing and comparing different techniques to analyze the pressure on both joints and muscles. The aim of the research is to gain a better understanding of how we use our bodies in the tree and how potential injuries are sustained, including the mechanisms for longer-term injuries.

Arborists frequently complain of suffering from musculoskeletal injuries caused by repetitive stretching and supporting large loads in contorted postures. The prolonged use of these techniques can result in muscle sprains and degenerative joint problems. This project is investigating correlations between working practices and chronic injury rates to provide an evidence basis for the recommendation of safer working practices and improved healthcare for arborists. In turn, we hope this will enable better training and development of techniques for future generations, prompting a longer working life and reducing the drain on our skilled workforce.

Photo 3: Suiting up for a motion-capture climb.

Recent advancements in biomechanical-motion analysis equipment have enabled the measurement of three-dimensional human movement within environments that were previously inaccessible. Earlier motion analysis was performed using optical tracking equipment, which, while accurate, was unsuitable for use outdoors, and this excluded its application to tree climbing. Motion-capture equipment is now available that uses inertial tracking sensors and is operable in more realistic scenarios, such as within the canopy of a tree. With this kit, we aim to map a tree climber’s movements as they climb. The data then provides a body map showing the skeletal structure and muscle structure of the climber. We are recording different access and climbing methods to analyze the effect they each have on a climber’s body. We then plan to look at tasks in the tree and work-positioning options when undertaking those tasks.

Photo 4b: How the Biomechanics of Bodies, or BoB, software can highlight which muscles are being loaded in a particular work position.

The project set out to establish whether there are significant differences between arborists trained in traditional doubled- or moving-rope technique (DdRT/MRT), improved-friction-management MRT and modern, developing stationary-rope techniques (SRT). Climbing tasks to be investigated include, but are not limited to, access against the stem, free-hanging rope access, movement in the canopy to a pruning target, pruning cuts with a saw and descent from the tree. We hope to look at chain-saw work in time.

The Biomechanics Group at Coventry University in Coventry, England, has experience applying motion-capture
methods across a broad spectrum of applications, from sports-performance optimization through product design to
medical-device analysis. The Biomechanics Group has developed software capable of analyzing human motion and calculating the forces and torques developed within a person’s body during a diverse range of activities. Using it, correlations will be calculated between loads that occur at major joints within arborists’ bodies and the rate of musculoskeletal injuries.

To support this work with biomechanics, we are using online survey data from working arborists to ascertain their current working methods, the injuries they have suffered and whether they have made any changes to their working practices to reduce the chance of compounding injuries or problems. So far, all the evidence has been anecdotal, and we hope to gain some meaningful data to better understand the current problems and tree-worker climate.

Photos 4a: Climber’s movements being captured live

Live data capture

In summer 2018, we scheduled two days of testing with Barbara May and James Shippen from Coventry University, along with a climbing team. The first morning was spent testing the data-capture equipment, setting it up to ensure it did not compromise the climber’s ability to move freely or the functional and safe use of the climbing equipment. The afternoon was spent benchmarking climbing-ascent methods and techniques to start building up a dataset to study. (Photo 3)

That evening we all met to plan for the following day. We had proved the concept worked well and could see the results on screen. On day two, we expanded the datasets and looked at movement in the crown while branch walking.

Graph 1 shows the loads on the climbing line for SRT in green and MRT in red. We captured this data for all methods tested. During analysis, we found we had one big issue. Up until this point, the software and hardware have been used to study people who are in contact with the ground. A tree climber moving up a rope has their weight in the rope, harness, hands and feet, as well as in passing contact with the tree.

Graph 1. Loads on an arborist’s climbing line measured in kN while branch walking using SRT (green) and MRT (red). Photos and graphics courtesy of Alexander Laver.

Tracking these transferred loads to give a full and accurate picture of the muscle loading and torque in the joints is a major hurdle we need to overcome. However, from the captured datasets, we now can model the methods and compare these using nominal loads. This part of the work will rely on the observation and experience of a climber to inform us where the connected load distributions are felt in the body while moving around the system. This will demonstrate the theory but will not give us full, reportable science, just anecdotal interpretation. (Photos 4a & 4b)

Graph 2: Reported sites of injury and pain caused by climbing activities from 277 respondents.

Online survey of climbers

We ran an online survey asking key questions of people in the tree care industry. With more than 325 responses and a good, broad dataset, we have made some clear discoveries. The main conclusion we can draw is that tree climbers do indeed suffer from muscular and skeletal injuries, but there are also patterns of common areas where people get injured.

We asked, “Have you ever suffered any muscular or skeletal injuries or pain caused by climbing activities?” Of the 315 people who answered the question, 273 (86.67%) said yes. Those who answered yes were then asked to specify where the injuries or pain occurred. The results from the 277 who replied appear in Graph 2. No data was gathered as to the extent of the pain or injuries caused, nor information relating to the duration of work, nor background on previously carried injuries and so on; we may try a follow-up survey to see if we can dig deeper into these issues.

Next steps

Work on quantifying the unknown key loads on a climber’s hands, feet and harness is ongoing. The load cells currently available for this project, even though designed for rope-load measurements, are just too big to add into a harness system without changing the climbing system’s ergonomics to the point and therefore affecting the true picture. To this end, I am working on installing small strain gauges to items of climbing equipment and developing small microprocessors to capture the data. Once we have some working prototypes of these instruments, we can work on software to sync the data to motion-capture data in Mat Lab to give us a fuller picture. From there, we can look at new, complete datasets of the hot-spot areas where we have identified the greatest risks to the climbers as a result of certain movements or techniques.

Phillip Kelley is a safety team leader at Wright Tree Service, Inc., a 43-year TCIA member company based in Des Moines, Iowa.

Alexander Laver, BCMA, is the founder of Tree Logic, an arborist training company based in Great Dunham, Norfolk, United Kingdom. He is an NPTC assessor, Lantra registered trainer, and LOLER inspector. Some content from Laver’s portion of this article first appeared in the Winter 2019 issue of Arb Magazine, the publication of the Arboriculture Association (UK).

This article was based on Phillip Kelley’s presentation on the same subject at TCI EXPO 2019 in Pittsburgh, Pennsylvania. To listen to an audio recording of that presentation, go to this page in the digital version of this issue of TCI Magazine online, under the Publications tab, and click here.

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