A descriptive analysis of the climbing mechanics of a mountain goat (Oreamnos americanus)

A descriptive analysis of the climbing mechanics of a mountain goat (Oreamnos americanus)

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ARTICLE IN PRESS

ZOOL-25518; No. of Pages 6

Zoology xxx (2016) xxx–xxx

Contents lists available at ScienceDirect

Zoology journal homepage: www.elsevier.com/locate/zool

A descriptive analysis of the climbing mechanics of a mountain goat (Oreamnos americanus) Ryan T. Lewinson a,b,c,∗ , Darren J. Stefanyshyn a,b a b c

Schulich School of Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1N4, Canada Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1N4, Canada Cumming School of Medicine, Foothills Campus, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada

a r t i c l e

i n f o

Article history: Received 9 October 2015 Received in revised form 1 February 2016 Accepted 1 June 2016 Available online xxx Keywords: Climbing ability Climbing kinematics Biomechanics Mountain Ungulates Incline

a b s t r a c t The mountain goat (Oreamnos americanus) is one of the most extraordinary mountaineers in the animal kingdom. While observational descriptions exist to indicate factors that may influence their climbing ability, these have never been assessed biomechanically. Here, we describe whole-body motion of a mountain goat during ascent of a 45◦ incline based on a video recording in the Canadian Rocky Mountains, and discuss the results in a mechanical context. During the push-off phase, the hindlimb extended and the forelimb was tucked close to the torso. During the pull-up phase, the hindlimb was raised near to the torso, while the forelimb humerus seemed to “lock” in a constant position relative to the torso, allowing the elbow to be held in close proximity to the whole-body center of mass. Extension of the elbow and carpal joints resulted in a vertical translation of the center of mass up the mountain slope. Based on the observations from this naturalistic study, hypotheses for future controlled studies of mountain goat climbing mechanics are proposed. © 2016 Elsevier GmbH. All rights reserved.

1. Introduction The mountain goat, Oreamnos americanus (de Blainville, 1816), is an alpine ungulate whose current range extends throughout the mountainous regions of North America from Alaska to Colorado. This species is uniquely adapted to thrive in some of the most extreme climates and terrains on the planet, regularly spending its time at temperatures near −50 ◦ C, with wind speeds over 100 km/h, on elevations over 4,000 m and on slopes in excess of 60◦ (Chadwick, 1983). As a consequence of its remoteness, there has been very little research conducted on the mountain goat. Of the research that has been conducted on mountain goats, a vast majority has been on population dynamics and conservation (Chadwick, 1983; Festa-Bianchet and Côté, 2008; Shafer et al., 2012). Despite this animal’s reputation as being one of the most qualified mountaineers in North America, very little research is available to explain the mechanics of how the mountain goat actually accomplishes its climbing movements. In large part, this is due to the fact that their regular habitat is mostly inaccessible to humans, making sightings rare, and recording of naturalistic climb-

∗ Corresponding author at: Cumming School of Medicine, University of Calgary, 3330 Hospital Drive NW, Calgary, AB, T2N 4N1, Canada. E-mail address: [email protected] (R.T. Lewinson).

ing motions challenging. Consequently, limited naturalistic data exists upon which further controlled studies on captive populations may be conducted. The mountain goat is a member of the Caprinae subfamily of Bovidae; however, mountain goats are considered distinct from other members of Caprinae, given that, based on available fossil records, the mountain goat seems to have evolved over 100,000 years ago. Their closest extant relative residing in similar mountainous terrain is believed to be the chamois (Rupicapra rupicapra). Comparatively, it is noted that the mountain goat is far more muscular, especially in the shoulder and neck region, than the chamois, and the mountain goat is known for its short, stocky limbs and prominent muscular shoulder hump (Chadwick, 1983). Even compared to other North American climbers such as the bighorn sheep (Ovis canadensis), the mountain goat appears built for tactical climbing, with a low center of mass (COM), and a fairly thin body when viewed anteriorly, perhaps to help it climb narrow ledges (Smith, 2014). Chadwick (1983) described the mountain goat’s forequarters as “disproportionately massive,” and also described the mountain goat as having a low, anterior COM, a large neck, and tremendously developed shoulder musculature, which all lend themselves to effective climbing. However, an assessment of the actual mechanics of mountain goat climbing has not yet been conducted. One study investigated the energetics of mountain goat walking vs. bighorn sheep walking, and found that mountain goats

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Fig. 1. All 9 frames from the climbing movement are shown. The first 6 frames describe the push-off phase of climbing, where the hindlimb is in contact with the mountain surface. The final 3 frames represent the pull-up phase. Center of mass positions are shown by the open dot.

were extremely efficient from a metabolic perspective when in deep snow (Dailey and Hobbs, 1989). Anatomically, they noted that mountain goat brisket height was much lower than that of bighorn sheep, and that mountain goat hoof area was bigger. Energetically, mountain goats tended to plow through deep snow, while bighorn sheep tended to bound, and in both cases the animals were generally less efficient than other ungulates. While highlighting differences between two of North America’s premier climbers, this was done on captive populations outside of their natural cliff-side habitat and did not assess climbing movements specifically, nor in a whole-body mechanics context. Given the insufficient naturalistic data upon which hypotheses for controlled studies with captive populations can be based, we sought to (i) outline a method for evaluating mountain goat biomechanics using field-based video data, (ii) provide a preliminary descriptive kinematic analysis of the climbing movement of a mountain goat, and from this, (iii) provide hypotheses that could be tested further in controlled studies as to possible movement kinetics. Given that previous observational reports suggest that the large shoulder musculature of mountain goats anatomically separates it from other mountain ungulates, and consequently may contribute towards its climbing ability, it was hypothesized that the mountain

goat’s body rotations would primarily occur at the approximate location of the scapulohumeral joint during climbing.

2. Materials and methods A publically available video was obtained from YouTube.com (https://www.youtube.com/watch?v=EohJPi5iYPs). The original videographer of this video also provided the authors with written permission to utilize and reproduce the video. The video was obtained at a sampling rate of 15 Hz, and was originally filmed in the Canadian Rocky Mountains. The animal under study was wild, and therefore this was a naturalistic observational study, not a controlled experiment. The climbing movement selected for analysis was in essence a series of galloping leaps − the animal would push off with its hindlimbs, catch the mountain with its forelimbs, propel itself up the slope and then repeat. A representative lateral view climbing motion was chosen for analysis from the video. All frames during the climbing motion were extracted, and assessed visually to define push-off (i.e. phase where the hindlimb was in contact with the slope) and pull-up (i.e. phase where the forelimb was in contact with the slope) phases of the climbing motion. All frames that comprised the full climbing movement then underwent image processing.

Please cite this article in press as: Lewinson, R.T., Stefanyshyn, D.J., A descriptive analysis of the climbing mechanics of a mountain goat (Oreamnos americanus). Zoology (2016), http://dx.doi.org/10.1016/j.zool.2016.06.001

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Fig. 2. A schematic diagram of the anatomical marker locations and joint/segment angles considered in this study. The points are as follows: hoof (M1 ), metacarpophalangeal joint center (M2 ), carpal joint center (M3 ), elbow joint center (M4 ), scapulohumeral joint center (M5 ), anterior torso (M6 ), tail (M7 ), hip joint center (M8 ), stifle joint center (M9 ), tarsal joint center (M10 ), metatarsophalangeal joint center (M11 ) and hindlimb hoof (M12 ). ␪1 represents the metacarpophalangeal joint angle, ␪2 represents the carpal joint angle, ␪3 represents the elbow joint angle, ␪4 represents the humeral angle, ␪5 represents the torso segment angle, ␪6 represents the hip joint angle, ␪7 represents the stifle joint angle, ␪8 represents the tarsal joint angle, and ␪9 represents the metatarsophalangeal joint angle. The dashed line starting at the anterior torso marker (M6 ) represents the horizontal, in relation to which the torso segment angle was determined. For details on the determination of joint centers and joint angles see Section 2 and the supplementary file in the online Appendix.

There were 9 frames of video (15 Hz) that comprised the full climbing motion, representing 0.54 seconds (Fig. 1). The first 6 frames defined the “push-off phase,” which we defined as the period where the mountain goat had extended its hindlimbs to propel its forelimbs and torso up and towards the mountain slope (i.e., only the hindlimb was in contact with the ground). Frames 7–9 described the “pull-up phase” of climbing, which we defined as the period where hindlimb push off had been completed, and the forelimbs were used to rapidly pull the body up the mountain slope (i.e. only the forelimb was in contact with the ground). Image processing firstly included removal of the image background. As the right limbs were not fully in view from the left lateral side of the mountain goat, they were also removed, and were assumed to be performing similar motions as the left limbs. This procedure was done manually (Microsoft Word 2013, Microsoft, Redmond, WA, USA). Images were then exported to Matlab v2015 (MathWorks, Natick, MA, USA) where they were converted to binary images (white represented the mountain goat and black represented background). To confirm this conversion, as well as confirm that the previous background removal was done in a similar fashion for all frames, the total white area was determined in Matlab. This area was held within 3% for the push-off phase frames, and within 2% for the pull-up phase frames. Allowing for some area change from frame to frame within the push-off or pull-up phases due to segment overlap with the torso, we believe these values supported our approach. Based on these areas, the center of area was calculated for each frame. Assuming a constant density throughout the body, which is similar to assumptions in human biomechanics research (Ackland et al., 1988), the center of area also represents the whole-body COM. Since the camera was not stationary, changes to the COM position were expressed relative to either the fore or rear limb hoof − whichever was in contact with the ground. Since the video was filmed in the summer months, after the mountain goat had completed shedding, error in this process due to excess wool was likely quite minimal. Fig. S1 in the supplementary online Appendix provides an overview of this analysis procedure. Joint centers and anatomical landmarks were defined visually for each frame in Matlab according to the conventions in Fig. 2. Segments were then defined by connecting adjacent points (Arnold

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et al., 2013). Specific details on segment definitions are found in the supplementary file in the online Appendix. This procedure was performed 5 times for each frame to minimize error from visual landmarking; the average joint center locations across the 5 trials for each frame were used in subsequent analyses. Joint angles were calculated as absolute values rather than relative to a neutral orientation using the positions of neighboring markers (Fig. 2). Details on angle definitions are found in the supplementary file in the online Appendix. However, of particular importance is the fact that the humeral angle was defined as an angle of the humerus relative to the torso, and not of the actual scapulohumeral joint. Without more sophisticated equipment and controlled testing environments, determination of the scapula orientation is quite challenging in quadrupeds. Additionally, since the scapula has no bony landmark that is constant (i.e. the skin, muscle and wool can glide over the scapula), identification of a precise location of the scapula was not possible in the present study. Consequently, our analysis does not account for actual angles of the scapulohumeral joint, nor the angular orientation of the scapula on the torso; however, it is likely that changes to the scapulohumeral angle were relatively small, as is the case for other quadrupeds (Goslow et al., 1981; Fischer et al., 2002). Consequently, if angular change existed at the humeral angle, likely this reflected an angular change of the scapula and shoulder girdle itself rather than the scapulohumeral joint. Similarly, if the humeral angle did not change, it would be likely that angular change at the scapula was not occurring, or occurring minimally. Since the scapula is anchored to the humerus, it was possible to determine approximations of shoulder translational movements such as protraction, retraction, depression and elevation. Torso angular velocities were determined by calculating the difference in angular position between adjacent frames, and dividing by the difference in time between frames. Therefore, this procedure yielded velocity values that occurred at a time point in between each of the 9 frames. The position of instantaneous center of rotation of the torso was calculated in Matlab by determining the linear velocity of the anterior torso marker (from translational x and y coordinates from one frame to the next), and then dividing by torso angular velocity (Beer et al., 2009). These values were then subtracted from the anterior torso horizontal and vertical positions on the image to give the coordinates of the instantaneous center of rotation. The mountain goat under study was a male, estimated to be about 2 years of age based on horn length (Smith, 1988), which would make this particular goat a young adult. It was assumed that the mountain goat’s height at the scapulohumeral joint during normal standing would be 0.75 m, which is slightly less than the typical shoulder height of a full-grown male. By adding the pixel lengths of each of the forelimb segments, a total pixel length for the forelimb was determined. Equating this to 0.75 m, a pixel-to-meters conversion ratio could be determined (total pixel length/0.75 m = conversion ratio). This ratio was used to provide an estimate of coordinate locations in metric units. The angle of the mountain slope was determined from coordinates along the mountain slope, and then using trigonometry. This procedure estimated the slope to be about 45◦ . As the sample size was only n = 1, no statistical analyses were performed. Instead, all data are provided as raw values, and an interpretation of these results based on biomechanical theory is provided.

3. Results and discussion All joint angle data can be found in Fig. 3. During the push-off phase, joint extension can be noted at the tarsal, stifle and hip

Please cite this article in press as: Lewinson, R.T., Stefanyshyn, D.J., A descriptive analysis of the climbing mechanics of a mountain goat (Oreamnos americanus). Zoology (2016), http://dx.doi.org/10.1016/j.zool.2016.06.001

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Fig. 3. Angular position data for the torso and fore/hindlimb joints throughout the climbing motion. Sections in grey represent the push-off phase, while the sections in black represent the pull-up phase.

joints of the mountain goat hindlimb, while the metatarsophalangeal joint underwent a small amount of flexion. This flexion likely occurred eccentrically due to body weight and large ground reaction forces. In the forelimb, a trend towards carpal joint and elbow joint flexion, and humeral joint extension could be observed. Additionally, a decrease in distance between the scapulohumeral marker and anterior torso marker of 14.1 pixels (∼10.1 cm) was observed, due to a combination of scapulohumeral protraction and elevation. Together, these movements allowed the mountain goat to propel its body towards the mountain, and tuck its forelimb close to the torso. This procedure of tucking the forelimb likely allowed

the mountain goat to maintain its COM as close to the mountain face as possible. Throughout the pull-up phase, the mountain goat seemed to “lock” its humerus at a fairly constant angle relative to its torso, with only very minimal humeral flexion. This finding is consistent with those observed in other quadrupeds during level locomotion, where the humerus is roughly horizontal to the torso during the late stance phase of the forelimb (Fischer et al., 2002). The distance between the scapulohumeral and anterior torso marker increased over the duration of the pull-up phase. Specifically, after adjusting for torso rotation, an estimated 6.9 pixels (∼4.9 cm) of scapulohumeral depression and 2.4 pixels (∼1.7 cm) of scapulohumeral

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retraction was found. The metacarpophalangeal joint also experienced minimal angular change across the pull-up phase, but slight extension can be noted. The majority of joint angular motion in the forelimbs across the pull-up phase was found at the carpal joint and elbow joint, where joint extension can be clearly observed in both cases. In the hindlimb, flexion could be seen in each of the metatarsophalangeal, tarsal, stifle, and hip joints, allowing the mountain goat to raise its hindlimb and begin the next climbing cycle. During the push-off phase, the whole-body COM translated relative to the hindlimb hoof by a vertical distance of 67.9 pixels (∼48.4 cm), and by a horizontal distance (i.e. along the image horizontal axis towards the mountain face) of 53.7 pixels (∼38.3 cm). During the pull-up phase, the whole-body COM was found to experience vertical and horizontal translation of 33.0 pixels (approximately 23.6 cm) and 20.8 pixels (approximately 14.9 cm), respectively. Additionally, in each of the frames in the pull-up phase, the COM was found to be in very close proximity to the elbow joint center location (distance between both markers had a range of 22.2 pixels to 21.2 pixels, about 15.2 cm). This approach likely allows extension of the elbow and carpal joints to directly modulate the height of the body COM, rather than rotating the torso. Based on anterior torso and tail marker locations across the push-off phase, torso angular velocity was determined to increase from −163◦ /s (i.e. rotating away from the mountain) between frames 1 and 2, to 67.9◦ /s (i.e. rotating towards the mountain) between frames 5 and 6. Additionally, the length of the torso increased by 15.8 pixels (∼11.3 cm) throughout the push-off phase. Since the push-off phase was characterized by hindlimb extension and humeral extension of the forelimb towards the mountain face, this increase in torso length could indicate that the mountain goat extends joints in the spine to gain additional height during pushoff. During the pull-up phase, angular velocity of the torso segment was determined to decrease from 79.4◦ /s (i.e. rotating towards the mountain) between frames 7 and 8, to 59.4◦ /s between frames 8 and 9. The length of the torso segment remained unchanged across the pull-up phase with a range of 95.4–97.6 pixels (∼68.7 cm), suggesting similar spinal orientations during the pull-up phase. This torso length was shorter than the maximum torso length that occurred in frame 6 of the pull-up phase by about 20 pixels (14.3 cm). Therefore, the torso experienced an angular acceleration towards the mountain face during the push-off phase, and an angular deceleration during the pull-up phase. This change in angular velocity throughout the movement cycle suggests a change in the mountain goat’s angular momentum. If the torso and hindlimbs are assessed as a single segment, it is also probable that the mass moment of inertia was reduced during the pull-up phase (Beer et al., 2009) due to the animal raising its hindlimbs towards its torso, which has been shown to occur previously (Kilbourne and Hoffman, 2013). During the push-off phase, a propulsive impulse would have been produced at the hindlimb hooves (Arnold et al., 2013), inducing a net torque about the torso axis of rotation. While the present analysis is based on a series of successive climbing movements, the propulsive impulse notion is consistent with other work on jumping in dogs, where it was found that the hindlimbs produce a large amount of positive work (Alexander, 1974). A critical point for consideration is that torso rotation did not appear to occur primarily about the whole-body COM, nor about a location near to the scapulohumeral joint marker as originally hypothesized. Based on our calculations, it was found that the average location of the instantaneous center of rotation for the torso segment across the push-off and pull-up phases was located 13.8 pixels superior on the image vertical axis (∼9.8 cm) and 81.4 pixels anterior on the image horizontal axis (∼58.0 cm) relative to the anterior torso marker – well forward of the mountain goat’s torso, and approximately at the location of the mountain goat’s head. This finding highlights

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the mountain goat’s ability to produce a strong propulsive impulse during the push-off phase, as well as produce immense muscular force during the pull-up phase to propel its torso up the mountain slope. Based on rudimentary analytical inverse dynamics assessment during the pull-up phase (see the supplementary file in the online Appendix), it is likely that an extension torque was produced at the scapulohumeral joint. Given the humeral angle relative to the torso was quite constant, and the scapulohumeral joint generally undergoes minimal angular change in quadrupeds (Fischer et al., 2002), this anchoring of the shoulder in an angular sense may allow the mountain goat to optimize the use of its powerful shoulder, neck and back muscles to elevate and rotate the torso as a whole, rather than modulate the angular position of the scapula and forelimb. This type of opposite muscle action has been shown in humans as well, where activity of the pectoralis major muscle can be utilized to expand the rib cage during breathing when the arm is anchored in position (Kim et al., 2012). Of course, in the case of the mountain goat, this would also mean that in addition to muscles contracting to raise and rotate the torso as a whole, powerful muscle contraction must also be generated to maintain the shoulder in a fairly constant position. As examples, the serratus ventralis thoracis and cervicis may contract to raise the torso toward the scapula, or stabilize the scapula, respectively, and rhomboideus may help reduce the angle between the torso and neck (Payne et al., 2005). The finding that scapulohumeral depression occurred during the pull-up phase, despite the forelimb remaining in contact with the ground, supports this concept, as it would indicate the torso is drawn vertically away from the scapulohumeral joint. This may be a possible explanation as to why the mountain goat has disproportionately massive shoulder and neck musculature, with a prominent shoulder hump (Chadwick, 1983). Alternatively, it may also be possible that a sufficiently large angular momentum is maintained from the push-off phase (potentially through the action of raising its hindlimbs), which allows the mountain goat to passively rotate up the slope, and use its forelimb more for stability. The present study is limited by the possibility that the visual detection of anatomical locations may have varied from frame to frame; however, the use of multiple analysis trials likely helped to minimize this error. Moreover, the shoulder joint was not fully accounted for, as only the humeral angle relative to the torso was studied, which may not truly represent the scapulohumeral actions and does not account for scapula angular movements. This is primarily of importance during the pull-up phase of the climbing motion. Since it was found that the humeral angle remained fairly constant during this period, scapula angular motions not accounted for in the present study are likely not large. Importantly, the sampling rate of the video was very low, and so estimations of angular velocities and accelerations, and thus instantaneous centers of rotation could be inaccurate. Additionally, the specific lens used to capture the video is not known, and based on the video it appears the videographer is below the animal during the climb. Consequently, error due to parallax is a possibility. Lastly, and most importantly, only one mountain goat was analyzed, and in an uncontrolled, observational fashion. As a result, it is not known if all mountain goats show the same movement pattern, or how this movement pattern changes in regards to the mountain slope the animal is climbing. With additional animals studied, it is possible that some of the trends identified here may be determined as significant, or that no effect would be seen on average. Given the relatively low population numbers and the extreme habitat of the mountain goat, capturing multiple naturalistic videos of different goats in similar climbing situations would be extremely challenging. Therefore, we believe the current analysis on one animal is of value as a preliminary account of the basics of mountain goat climbing mechanics, despite the limitations associated with this

Please cite this article in press as: Lewinson, R.T., Stefanyshyn, D.J., A descriptive analysis of the climbing mechanics of a mountain goat (Oreamnos americanus). Zoology (2016), http://dx.doi.org/10.1016/j.zool.2016.06.001

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small sample size. Since this work is the first on mountain goat climbing, and thus meant to be exploratory rather than conclusive, we believe that the use of a single video observation in a naturalistic setting is appropriate for providing future research hypotheses, which may be explored in more detail and with more advanced equipment on larger sample sizes in captive populations. In conclusion, this study has provided the first known documentation of the biomechanics associated with mountain goat climbing. In previous literature, most of the attention is directed towards shoulder strength as a factor that affects the climbing ability of the mountain goat (Chadwick, 1983; Smith, 2014). The present analysis highlights that there are a number of features that may be important for further and more detailed investigation. Specifically, based on the present analysis, we hypothesize for future studies that (i) generation of a propulsive impulse from the hindlimbs is the major contributor to push-off phase success in climbing, (ii) “locking” the humerus and scapula in an angular sense to align the elbow joint and lower forelimb with the whole-body COM allows the mountain goat to directly modulate its COM height during the pull-up phase, and (iii) shoulder and neck musculature greatly contribute to the mountain goat’s ability to propel its torso up a slope during the pull-up phase. From an evolutionary perspective, these actions may explain why the mountain goat has such massive shoulder musculature with a prominent shoulder muscle hump. Together, these factors appear to contribute towards the mountain goat’s ability to ascend a steep mountain slope, but should be assessed in more detail in future controlled studies with larger sample sizes and more sophisticated analysis equipment, specifically to investigate individual joint kinetics, and to gain a better understanding of mountain goat angular momentum during the climbing movement. Supplementary to this, more detailed accounts of mountain goat comparative anatomy are needed to gain a better understanding of the specific muscular adaptations mountain goats have developed to excel in their mountainous habitat.

Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.zool.2016.06.001. References Ackland, T.R., Hensen, P.W., Bailey, D.A., 1988. The uniform density assumption: its effect on estimation of body segment inertial parameters. J. Appl. Biomech. 4, 146–155. Alexander, R., 1974. The mechanics of jumping by a dog (Canis familiaris). J. Zool. 173, 549–573. Arnold, A.S., Lee, D.V., Biewener, A.A., 2013. Modulation of joint moments and work in the goat hindlimb with locomotor speed and surface grade. J. Exp. Biol. 216, 2201–2212. Beer, F.P., Johnston, E.R., Cornwell, P.J., 2009. Vector Mechanics for Engineers: Dynamics, 9th ed. McGraw-Hill, New York. Chadwick, D.H., 1983. A Beast the Color of Winter. Sierra Club Books, San Francisco. Dailey, T.V., Hobbs, N.T., 1989. Travel in alpine terrain: energy expenditures for locomotion by mountain goats and bighorn sheep. Can. J. Zool. 67, 2368–2375. de Blainville, H.M.D., 1816. Sur plusieurs espèces d’animaux mammifères de l’ordre des ruminants. Bull. Soc. Philom. Paris, 73–82. Festa-Bianchet, M., Côté, S.D., 2008. Mountain Goats: Ecology, Behavior, and Conservation of an Alpine Ungulate. Island Press, Washington D.C. Fischer, M.S., Schilling, N., Schmidt, M., Haarhaus, D., Witte, H., 2002. Basic limb kinematics of small therian mammals. J. Exp. Biol. 205, 1315–1338. Goslow, G.E., Seeherman, H.J., Taylor, C.R., McCutchin, M.N., Heglund, N.C., 1981. Electrical activity and relative length changes of dog limb muscles as a function of speed and gait. J. Exp. Biol. 94, 15–42. Kilbourne, B.M., Hoffman, L.C., 2013. Scale effects between body size and limb design in quadrupedal mammals. PLoS One 8, e78392. Kim, K.S., Byun, M.K., Lee, W.H., Cynn, H.S., Kwon, O.Y., Yi, C.H., 2012. Effects of breathing maneuver and sitting posture on muscle activity in inspiratory accessory muscles in patients with chronic obstructive pulmonary disease. Multidiscip. Respir. Med. 7, 9. Payne, R.C., Veenman, P., Wilson, A.M., 2005. The role of the extrinsic thoracic limb muscles in equine locomotion. J. Anat. 206, 193–204. Shafer, A.B., Fan, C.W., Cote, S.D., Coltman, D.W., 2012. (Lack of) genetic diversity in immune genes predates glacial isolation in the North American mountain goat (Oreamnos americanus). J. Hered. 103, 371–379. Smith, B.L., 1988. Criteria for determining age and sex of American mountain goats in the field. J. Mammal. 69, 395–402. Smith, B.L., 2014. Life on the Rocks: A Portrait of the American Mountain Goat. University Press of Colorado, Boulder, CO.

Acknowledgements The authors thank Nature Freak on YouTube for giving permission to utilize the video recording for analysis. R.T.L. was funded by a Vanier Canada Graduate Scholarship from the Canadian Institutes of Health Research, an award from the Natural Sciences and Engineering Research Council of Canada CREATE Program, a scholarship from the Killam Trusts, and an MD-PhD Studentship from Alberta Innovates − Health Solutions. Funding agencies played no role in study design, data collection, analysis, or drafting of this manuscript.

Please cite this article in press as: Lewinson, R.T., Stefanyshyn, D.J., A descriptive analysis of the climbing mechanics of a mountain goat (Oreamnos americanus). Zoology (2016), http://dx.doi.org/10.1016/j.zool.2016.06.001