Characterization Of Heel-Hook, Drop-Knee, And High-Step Movements In Climbers' Knees

Study design The research took place in the Ergonomics Laboratory at Pontificia Universidad Javeriana in the city of Bogotá, Colombia. An indoor climbing wall was constructed, and four Vicon T-Series cameras were strategically positioned within the capture area (Figure 1). Figure 1. Experimental setup where the climbing wall and the cameras used can be seen. To evaluate the effect of each climbing movement executed on a specific route, climbing holds were placed on the wall. For each movement, a set of holds was selected (Figure 2).

Figure 2. Climbing wall with colored holds representing the designated holds for each movement. The yellow holds indicate the heel-hook, the red holds indicate the drop-knee, and the green holds indicate the high-step. Markers were placed along the right leg of the participants as shown in Figure 3. A total of 19 reflective markers were utilized. This distribution was chosen to ensure that each segment of the leg had at least two markers to track the entire execution of each technique. The leg was divided into three segments: the thigh (upper leg), calf (lower leg), and foot. The length between the knee and the ankle was measured from the lower part of the patella to the lateral malleolus as reference, and the length between the ankle and the foot was measured from the lateral malleolus to the tip of the big toe (hallux). Figure 3. Marker positions used during motion capture on the right leg.

Two additional markers were placed on the climbing wall to obtain the horizontal vector generated between them (M₁ and M₂). Through motion capture analysis, three angles were identified: the knee joint angle of maximum flexion, the angle between the lower leg and the horizontal (φ), and the angle between the foot and the horizontal (α). These angles were calculated using vectors generated between two markers for each segment via the dot product (Equation 1), where θ (RT) is the thigh-to-horizontal angle, and M (MM) is the knee moment. An instrumented climbing hold was built using three strain gauges from the company Omega. These strain gauges were evenly placed every 120° on the screw and then embedded inside a climbing hold. The connection was concealed behind the wall (Figure 4). Subsequently, the climbing hold was calibrated for the z-axis and y-axis. The strain generated on the screw was measured using Ingemoduler, a tool specifically designed for processing strain gauge information and converting it into strain. Force was determined by analyzing the strain generated on the screw and applying the linear regression equations derived from the calibration process. For heel-hook, y-axis forces were lower (2.83% ± 1.61% BW) due to some readings near instrument noise, yielding n=4. Figure 4. (A) Instrumented screw with three strain gauges (Omega) at every 120°. (B) Instrumented climbing hold as seen from the climber's perspective. The climbers were instructed to warm up, and once the markers were in place, they were asked to perform each movement once maximally, following a 3-minute rest period to minimize fatigue. A rigid body diagram was created for each movement, allowing analysis of forces on the foot and angles measured through motion capture. By utilizing this diagram, the force and moment exerted on the knee during execution were determined (Figure 5). Figure 5. Rigid body diagram for the drop-knee movement showing forces, angles, and moment.

Statistical analysis was conducted using Microsoft Excel and Microcal Origin 6.0. The data obtained were assessed for normality using the Shapiro-Wilk test. For normally distributed data, paired t-tests were employed to determine statistical differences between movements (significance threshold: P < 0.05). No multiple-comparison corrections were applied. In cases where data did not follow a normal distribution, Kruskal-Wallis analysis was utilized.

Table 1 presents a summary of the participants' demographics and morphological measurements. All participants were male climbers with a right dominant leg. The data exhibiting the greatest variability was climbing time, with an average of 7.24 ± 6.35 years. The group included both novice and nationally elite climbers.

2C.Heel-Hook

For strain gauge calibrations, an adjacent averaging filter was applied to remove noise. After obtaining data for each mass, two linear regressions (three points each) were performed for the z-axis and y-axis: These R² values indicate significant correlation, validating the equations for force calculations. When calculating heel-hook forces, some participants recorded data not differing significantly from instrument noise; thus, only four y-axis measurements were obtained from eight participants. Average forces as percentages of body weight were 20.54% ± 7.92% (drop-knee) and 22.99% ± 5.26% (high-step) in the z-axis, and 5.77% ± 4.45% (heel-hook) in the z-axis. Y-axis forces: 18.51% ± 11.37% (drop-knee), 16.96% ± 5.36% (high-step), 2.83% ± 1.61% (heel-hook) (Figure 6). Figure 6. Force as percentage (%) of body weight in each movement for y- and z-axes. Data as mean ± SD. Knee joint angles (thigh-hip to calf-knee vectors at maximal force onset) were 43.93° ± 8.72° (drop-knee), 58.28° ± 19.26° (high-step), 69.17° ± 16.12° (heel-hook) (Figure 7). Figure 7. Maximum knee flexion angle (°). Data as mean ± SD.

Horizontal angles used wall markers (M₁-M₂ vector) with thigh (θ) and foot (α) segments, yielding knee moments: 68.83 ± 46.07 Nm (drop-knee), -37.45 ± 21.71 Nm (high-step), 1.83 ± 8.81 Nm (heel-hook). Positive values indicate counterclockwise moment (Figure 8). Figure 8. Knee moment (Nm). Data as mean ± SD. Significant differences (P < 0.05): ● Moment: drop-knee vs. heel-hook (P = 0.002); high-step vs. heel-hook (P = 0.00002). ● Knee angles: drop-knee vs. heel-hook (P = 0.003). ● Z-axis forces: drop-knee vs. heel-hook (P = 0.002); high-step vs. heel-hook (P = 0.0002). ● Z-axis % body weight: drop-knee vs. heel-hook (P = 0.0009); high-step vs. heel-hook (P = 0.000006). ● Y-axis heel-hook tests were not performed due to negligible data.

This study characterizes forces, moments, and angles in drop-knee, high-step, and heel-hook movements in climbers' knees. These movements are associated with knee injuries, underscoring the need to understand their mechanics for prevention strategies. Indoor research with artificial walls is relevant, as most injuries occur in indoor bouldering. Literature reports walking moments per unit mass of 0.458-1.265 Nm/kg. Study values ranged from -1.61 to 0.34 Nm/kg (mostly negative, counterclockwise). Magnitudes were similar to walking. These represent external moments from measured forces and segment lengths; comparisons to walking/internal torques (e.g., extensor: 100.9 Nm at 20°; flexor: 76.1 Nm at 20°) require caution due to methodological differences. The heel-hook was expected to show highest loads due to injury associations, but yielded lowest values (Table 2). X-axis forces (into/out of wall) were not measured, potentially underestimating heel-hook loads, as heel traction may involve x-axis components. Results are specific to the 90° wall; steeper angles likely increase demands. Lutter et al. associated drop-knee/high-step injuries with dynamic force peaks during hold transitions, not evident here. Z-axis knee forces ranged 0.01-0.34 × BW, lower than walking (2.1 ± 0.2 × BW). Drop-knee showed greatest flexion (43.93° ± 8.72°), with angles 35.08°-100.51° generally in safer ranges (<90°). Heel-hooks exceeded 100° in some cases. Study limitations This study has several limitations that should be considered when interpreting the findings. First, the sample size was relatively small and included only right-handed male climbers between 22 and 35 years of age, which limits the generalizability of the results to other populations, such as women, left-handed climbers, or older and younger athletes. In addition, participants varied in experience level, ranging from novice to nationally elite climbers, and the study was not designed or powered to analyze differences between experience groups. A second limitation is related to the experimental setup. Only one indoor climbing wall with a fixed height and a vertical (90°) inclination was used, which restricted the evaluation of movements performed on steeper or more complex walls. The relatively low height of the wall may have constrained movement execution for taller individuals, and using a single instrumented hold reduced the analysis to one specific contact configuration and phase of each movement, rather than capturing the full variability of climbing routes. A third limitation concerns the measurement of forces. The instrument held measured forces only in the y- and z-axes, while forces in the x-axis (towards and away from the wall) were not recorded. This is particularly relevant for the heel-hook, where substantial traction along the x-axis is likely and could lead to an underestimation of the total load acting on the knee joint. Moreover, for the heel-hook, some y-axis measurements were close to the noise level of the device, resulting in a reduced number of valid trials for that variable and limiting the robustness of the corresponding analyses.

Finally, the study focused on external forces, joint angles, and external moments at the knee, without directly assessing internal joint loads, ligament stresses, or muscle activation patterns. As a result, it is not possible to establish causal relationships between the measured variables and specific injury mechanisms. The present work should therefore be viewed as an initial characterization of the mechanical demands of drop-knee, high-step, and heel-hook movements, and future studies are needed to incorporate three-dimensional force measurements, detailed neuromuscular models, and stratification by experience level to provide a more comprehensive understanding of how these movements are associated with knee injuries in climbers.

This study provides initial quantitative data on the external forces, knee joint angles, and external moments generated during the execution of the drop-knee, high-step, and heel-hook movements. On average, the drop-knee and high-step produced external forces equivalent to approximately 20% of body weight at peak loading under the conditions tested. The drop-knee demonstrated the greatest knee flexion among the three movements, while the heel-hook exhibited distinct loading characteristics within the limits of the measurement setup. Interpretation of the heel-hook must be made with caution. In this study, forces were measured only in the y- and z-axes, and the wall geometry did not reflect common scenarios in which climbers typically perform heel-hooks. Because the X-axis components (traction, rotation, and abduction) are relevant for this movement but were not captured, the present findings do not fully characterize heel-hook loading. Further research is necessary to better understand the loading patterns and potential biomechanical factors associated with knee discomfort or injury during climbing. Important next steps include incorporating measurement of forces in all three axes, using motion-capture models that can quantify full joint rotations, and integrating analyses of muscle activation. Expanding the sample to include climbers of different experience levels, genders, and limb dominance would also improve generalizability. Although the forces and angles measured in this study were not extreme compared to values reported in other biomechanical contexts, a more complete understanding of rotational loading and multi-planar joint behavior is needed to determine how knee structures are stressed during climbing techniques. Strengthening muscles involved in knee flexion and extension (such as the quadriceps and hamstrings) remains broadly recommended in the literature, but should be interpreted as general guidance rather than a direct implication of our findings. Proper technique and controlled execution of movements may also help climbers better distribute load across the limbs involved. Overall, this study serves as an exploratory step toward characterizing knee joint loading in common climbing techniques. Continued efforts to develop more comprehensive biomechanical models will help clarify how forces are distributed across the knee and will support future research into technique optimization and injury prevention strategies.