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APPLIED SCIENCES

Three-Dimensional Takeoff Step Kinetics of Long Jumpers with and without a Transtibial Amputation

FUNKEN, JOHANNES1; WILLWACHER, STEFFEN1,2; HEINRICH, KAI1; MüLLER, RALF1; HOBARA, HIROAKI3; GRABOWSKI, ALENA M.4,5; POTTHAST, WOLFGANG1,6

Author Information
Medicine & Science in Sports & Exercise: April 2019 - Volume 51 - Issue 4 - p 716-725
doi: 10.1249/MSS.0000000000001853

Abstract

Long jump distance depends on the approach and the takeoff step, where the underlying biomechanics elicited by an athlete strongly affect performance. Previous studies have determined spatiotemporal parameters as well as joint and center of mass (COM) kinematics for the long jump in nonamputee athletes (1–3). However, the loads applied on the musculoskeletal system such as ground reaction forces (GRF), joint moments, and joint work are not well established for nonamputee athletes or athletes with a lower extremity amputation. This information can be used to improve training and rehabilitation protocols, prosthetic design, and health and safety regulations in Olympic and Paralympic sports.

Previous studies have analyzed the sagittal plane kinetics of the takeoff step of the long jump, including GRF, and joint moments, power, and energy for four nonamputee athletes (personal record [PR], 7.05–7.53 m) with a short approach (15 m) (4) and for 11 nonamputee athletes (PR, 6.56–7.99 m) with a full approach (5). The former showed that the ankle joint is the largest energy absorber and generator in the long jump takeoff step, whereas the latter found that the magnitude of the peak joint moments and the work of the takeoff leg are not related to jump distance. Willwacher and colleagues (6) recently determined sagittal plane GRF and calculated total joint and COM energy during the takeoff step for the long jump with a full approach for nonamputee athletes and athletes with a below the knee amputation (BKA). In competition, long jumpers with BKA use carbon fiber running-specific prostheses (RSP) to allow them to compete and jump. The best athletes with BKA jump using their affected leg for the takeoff step. Previous research has shown differences regarding spatiotemporal parameters, joint mechanics, and GRF application characteristics between athletes with bilateral BKA and nonamputee athletes (7,8) and also between the affected and unaffected leg of athletes with a unilateral BKA during running and sprinting (9–11). On the basis of the differences in running and sprinting biomechanics between the affected and the unaffected legs, it is likely that the takeoff step biomechanics of the long jump are also different between athletes with BKA and nonamputee athletes. In line with this assumption, Willwacher et al. (6) found that athletes with BKA had a slower run-up but a more effective takeoff step technique compared with nonamputees, which resulted in the same long jump performance between groups. The authors, furthermore, emphasize that COM energy and overall joint energy are fundamentally different between athletes with and without a BKA during the takeoff step. However, lower extremity joint moments and joint energy were not separated into different planes of movement. Thus, a differentiated description of the musculoskeletal loads is still missing for the takeoff step of the long jump for athletes with BKA.

Previous research of nonamputee sprinting has found that peak frontal moments in the hip and knee are smaller (20%–75%) but not negligible compared with the sagittal plane moments in the same joints (12–14). This underlines the important role of the hip abductors to provide body weight support and maintain balance (15). Although the long jump, such as sprinting, requires primarily sagittal plane movement and force production (1,16,17), the mechanics of the frontal and transverse planes, resulting from compensatory or stabilization movements, likely add to the athletes’ total musculoskeletal loading and potentially influence performance and injury risk. Nonsagittal joint loading, such as a high external knee adduction moment or impulse, is associated with degeneration and pain in the knee (18,19), which is the second most common injury region (30%) for jumping disciplines (20). A comprehensive analysis of frontal and transverse plane kinetics for the long jump takeoff step is however missing for nonamputee athletes as well as for athletes with lower limb amputations. Comprehensive three-dimensional (3D) kinetics of the long jump takeoff step for athletes with and without a BKA would provide important information for coaches and athletes to develop specific training strategies that either improve performance and/or prevent injuries due to overloading.

The purpose of this study was to quantify 3D takeoff step kinetics for athletes with and without a BKA during maximum distance long jumps. On the basis of previous studies, we hypothesize that 1) both groups of athletes will have a considerable (>25%) amount of frontal and transverse plane joint loading relative to the respective sagittal plane joint loading and 2) musculoskeletal joint loading, such as joint moments and work, will be different between athletes with versus without a BKA during the takeoff step.

METHODS

Participants and study design

Ten male athletes participated in the study—three participants had a BKA (mean ± SD age, 26.0 ± 1.7 yr; mass [including socket and prosthesis], 78.7 ± 9.8 kg; height, 1.83 ± 0.04 m; long jump PR, 7.43 ± 0.99 m), and seven participants were nonamputee athletes (age, 24.6 ± 2.5 yr; mass, 80.1 ± 6.2 kg; height, 1.82 ± 0.07 m; PR, 7.65 ± 0.65 m). On the day of data collection, all athletes reported that they were healthy and free of injury and gave written consent to participate. The study design was approved by the ethical committee of the German Sport University Cologne (GSU) (approval no. 040/2016). Data collection was conducted at GSU and the Japan Institute of Sport Sciences.

Data collection

Retroreflective markers were attached to specific anatomical reference points on the athlete’s body and prosthesis (6). Individual dimensions, including length and circumference of the lower and upper body segments, were measured. Standing height was measured with both legs loaded. The athletes performed an individual competition-specific warm-up before performing three to six maximum distance long jumps with a full run-up. Kinematic data were captured with a 3D motion capture system (Vicon, Oxford, UK) operating at 250 Hz (GSU) or 500 Hz (Japan Institute of Sport Sciences), respectively. Kinetic data were captured simultaneously by one force plate (Kistler Instrumente Corporation, Wintherthur, Switzerland) mounted flush with the floor operating at 1000 Hz. High-speed cameras (100 Hz; Basler, Ahrensburg, Germany) were used to visually ensure valid force plate strikes.

Model calculations

Kinematic and kinetic data were both filtered using a Butterworth filter (50 Hz cutoff, fourth order, recursive). Ground contact was determined with a 10-N threshold of the vertical GRF.

Inverse dynamic calculations were conducted with a mathematical rigid full body model (Dynamicus, Alaska, Institute of Mechatronics, Chemnitz, Germany). For the long jumpers with BKA, the model was modified and incorporated a prosthesis modeled as two rigid bodies connected by a ball joint. Body anthropometrics as well as the mass and dimension of the prosthesis served as input parameters to individualize the model for each long jumper. The prosthetic ankle joint in the BKA group refers to the point of highest curvature of the prosthesis (21), which coincides with the most posterior point of the prosthesis. Two markers attached to the medial and lateral edge of the highest curvature of the prosthesis were used to define the joint axis (6). We captured one trial for each athlete in a static erect position, and this served as a reference to define the anatomical joint axes. The external joint moments were described in the coordinate system of the distal segment. We calculated the lever arm length between the resultant GRF vector and the ankle, knee, and hip joint as the perpendicular distance between the force vector and the respective joint center. GRF impulses were calculated by integrating the respective GRF component over time. To avoid influences of landing technique or poor foot/prosthesis placement on the takeoff board, jump distance was defined as the theoretical distance between the most anterior point of the foot or prosthesis during the takeoff step and the intersection between the COM flight path and the level ground (22). Further details on the model and calculation of jumping distance are described by Willwacher et al. (6). The best trial with respect to the theoretical jump distance of each athlete was used for further analyses of the takeoff step.

Statistics

For testing the first hypothesis, we defined a threshold for joint moments and work based on values previously reported for sprint running (12,14,23). Frontal and transverse plane hip and knee joint moments and work were defined as considerable if they exceeded 25% of the respective sagittal plane loading. For testing the second hypothesis that compared athletes with and without a BKA, and because of the small sample size, a nonparametric Wilcoxon ranked sum test was conducted between groups, and the level of significance was set to 5%. In addition, the percentage differences between the athletes with a BKA compared with the nonamputee athletes are presented.

RESULTS

All athletes with BKA used their affected leg as their takeoff leg. Mean jump distances were 7.26 ± 0.77 m for athletes with BKA and 7.27 ± 0.45 m for nonamputee athletes. Contact times for the takeoff step were 124 ± 14 ms for athletes with BKA and 122 ± 9 ms for the nonamputee athletes.

GRF

The shape of the vertical and horizontal GRF curves was different between the takeoff leg of athletes with BKA and nonamputee athletes (Figs. 1 and 2). The peak horizontal (anteroposterior) braking GRF for athletes with BKA (15.17 ± 3.68 N·kg−1) was 52.3% lower than that of the nonamputee athletes (31.79 ± 13.68 N·kg−1), but the peak horizontal propulsive GRF was not different (see Table, Supplemental Digital Content 1, Contact times and GRF values, https://links.lww.com/MSS/B460). Although the nonamputee athletes had a pronounced peak force in the lateral direction (10.48 ± 4.65 N·kg−1), athletes with BKA had near zero force production and GRF impulse in the mediolateral direction. In the vertical direction, the nonamputee athletes elicited an impact and active peak, whereas athletes with BKA elicited a single peak vertical force. There were no statistical differences in peak vertical GRF or vertical impulse between athletes with BKA (55.02 ± 10.03 N·kg−1, 4.55 ± 0.30 N·s·kg−1) and athletes without BKA (79.20 ± 23.64 N·kg−1, 4.08 ± 0.75 N·s·kg−1) because of the high between-subject variability within the nonamputee group. However, peak vertical GRF was 30.5% lower in value, but vertical impulse was 11.5% greater in value in athletes with BKA compared with nonamputee long jumpers.

F1
FIGURE 1:
Horizontal (left), mediolateral (middle), and vertical (right) GRF over the percentage of the stance phase for athletes with BKA (n = 3, red) and nonamputee athletes (n = 7, black). Values are normalized to body mass.
F2
FIGURE 2:
Schematic drawing of the GRF vector orientation and magnitude in the sagittal (top) and frontal (bottom) plane for the athletes with BKA (red—bottom panels) and the nonamputee athletes (black—top panels).

Joint moments

All sagittal, frontal, and transverse plane external peak hip and knee joint moments were smaller in athletes with BKA compared with the nonamputee athletes, except for knee abduction and external rotation. The (prosthetic) ankle dorsiflexion moment of the athletes with BKA was the only moment that was greater (206%) than that of the nonamputee athletes. In the sagittal plane, the hip and knee joints had greater (~83%–155%) peak flexion than extension moments for both groups of athletes (Table 1). However, only the difference between peak knee flexion versus extension moment for the nonamputee athletes reached the level of significance (P = 0.047). During the first 10% of ground contact, the nonamputee athletes elicited a knee extension moment, which was not present in the athletes with BKA (Fig. 3). Nonamputee athletes elicited a flexion hip joint moment during the first 40% of ground contact and an extension moment during the last 30% of ground contact, whereas athletes with BKA had a flexion moment during 94% of ground contact.

T1
TABLE 1:
Peak joint moments.
F3
FIGURE 3:
Ankle (top), knee (middle), and hip (bottom) joint moments for the sagittal (left), frontal (middle), and transverse (right) planes over the percentage of stance for athletes with BKA (n = 3, red) and nonamputee athletes (n = 7, black). Values are normalized to body mass and body height.

The ankle plantarflexion moment showed values of zero for the prosthetic ankle joint and negligible small mean values for the biological ankle of the nonamputee athletes during ground contact. The ankle dorsiflexion moment, however, was 3.1-fold higher in the prosthetic compared with the biological ankle joint. In the frontal and transverse planes, the ankle joint of the nonamputee athletes had eversion and external rotation moments, whereas the prosthetic ankle joint of the athletes with BKA had inversion and internal rotation moments (Fig. 3). Athletes with BKA had knee joint abduction and external rotation moments, whereas the nonamputee athletes had knee abduction and external rotation moments, followed by knee adduction and internal rotation moments. Peak frontal and transverse hip joint moments of the athletes with BKA were between 75.5% and 90.3% lower compared with those of the nonamputee athletes (Table 1).

Peak hip and knee joint moments in the frontal plane of both groups exceeded a value of 25% relative to the respective sagittal plane peak joint moments (BKA, 49%–83%; nonAMP, 33%–75%). None of the transverse peak joint moments of the hip and knee exceeded the defined threshold of 25% relative to the respective sagittal plane peak joint moment (BKA, 8%–15%; nonAMP, 9%–13%).

The length of the lever arm between the resultant GRF and the lower extremity joints averaged over the duration of ground contact was significantly different between the groups for all three joints (Fig. 4). Athletes with BKA had a 155.6% greater lever arm between the prosthetic ankle joint and the resultant GRF force vector compared with the biological ankle joint of the nonamputee athletes, but they had 57% and 54.2% shorter lever arms at the knee and hip joint, respectively.

F4
FIGURE 4:
Lever arm length between the resultant GRF vector and the ankle (left), knee (middle), and hip joint center (right) averaged over the duration of ground contact of athletes with BKA (n = 3, red) and nonamputee athletes (n = 7, black). Dashed lines indicate mean (SD) values.

Joint work

With the exception of the sagittal plane joint work of the prosthesis/ankle, joint work was lower in all joints and planes of motion for athletes with BKA compared with the nonamputee athletes (Fig. 5, see also Table, Supplemental Digital Content 2, joint work, https://links.lww.com/MSS/B461). Sagittal plane hip joint and frontal plane knee joint energy generation, however, were lower in value but not significantly different between groups because of the high between-subject variability within the nonamputee group. In the prosthetic ankle joint of the athletes with BKA, the sagittal plane energy absorption was 85% and return was 76.2% of the total sagittal plane joint absorption (5.12 J·kg−1) and generation/return (4.65 J·kg−1), respectively. The nonamputee long jumpers had more evenly distributed sagittal plane joint energy, where hip joint absorption was 27.7% and generation/return was 29.6%, knee joint absorption was 39.8% and generation/return was 30.3%, and ankle joint absorption was 32.5% and generation/return was 40.1% of the total sagittal plane joint work. In the nonamputee athletes, a significant amount of energy was absorbed (0.99 J·kg−1) and generated (0.87 J·kg−1) in the frontal plane of the hip and to, a lower extent, in the knee, whereas the frontal plane joint work of athletes with BKA was much lower (hip, factor of 4.0–6.6; knee, factor of 3.0–3.6) compared with the nonamputees. For both groups of athletes, most of the transverse plane joint work was much lower (50%–99.8%) compared with the other planes of movement but was higher (factor of >4) for the nonamputees compared with athletes with BKA.

F5
FIGURE 5:
Ankle, knee, and hip joint energy absorption (black) and generation/return (gray) for the sagittal (top), frontal (middle), and transverse (bottom) planes of athletes with BKA (n = 3, left) and nonamputee athletes (n = 7, right). Values are normalized to body mass.

Except for hip transverse plane energy generation for the athletes with BKA (2%) and hip transverse plane energy absorption (19%) of the nonamputee athletes, all energy changes in the hip exceeded a value of 25% relative to the respective sagittal plane joint energy changes in both groups (BKA, 25%–216%; nonAMP, 28%–68%). For both groups, none of the energy changes in the knee exceeded the defined threshold of 25% relative to the respective sagittal plane joint energy changes (BKA, 3%–20%; nonAMP, 6%–11%).

DISCUSSION

The purpose of this study was to quantify the 3D joint loads applied on the musculoskeletal system of athletes with and without a BKA during the takeoff step of the long jump. Although the hip and knee joints were considerably loaded in the frontal plane during the takeoff step for both groups of athletes relative to their sagittal plane joint loading (>25%), the transverse plane loading seems to play a minor role. Thus, we partially reject our first hypothesis that both athletes with and without a BKA would have considerable frontal and transverse plane joint loading compared with sagittal plane joint loading.

Most peak joint moments, as well as joint energy absorption and generation, were significantly different between the two groups. In sum, the absolute values of joint loading show that the long jump takeoff step of athletes with BKA is dominated by sagittal plane movements, whereas the long jump takeoff step of nonamputee athletes involves sagittal plane movements and joint work in the frontal plane. We accept our second hypothesis that the musculoskeletal joint loading is different between athletes with and without a BKA during the takeoff step.

GRF

The horizontal GRF and the vertical GRF of the nonamputee athletes are similar to results from previous research on nonamputee long jump (5). By contrast, the GRF and impulses of the athletes with BKA are similar to the half-sinusoidal force trace of a spring-mass model (24) or the springlike movements of wallabies (25). The prominent impact peaks in the first 20% of stance for the braking and vertical GRF reached mean values of approximately 2.5 and 6.3 kN, respectively, for the nonamputee athletes. In a study on nine human knee–foot–ankle specimens, dynamic impact forces between 11.4 and 17.9 kN applied to the plantar surface of the foot led to intra-articular fractures of the calcaneus (26). Another study including 50 specimens of the human lower limb predicted a 50% injury probability for plantar contact forces of 9.3 kN (27). The best nonamputee long jumper in our study reached peak GRF of 5.1 kN in the horizontal braking and 10.4 kN in the vertical directions during the takeoff step and, thereby, reached the critical level of impact forces reported for injury in human lower limb specimens. Although results from in vitro studies may not be fully applicable to an in vivo foot–ankle complex of a well-trained long jumper, our results can serve as one possible explanation for the increased incidence of ankle injuries, which comprise approximately 30% of all injuries among athletic jump disciplines in nonamputee athletes (20).

There were minimal mediolateral GRF elicited by athletes with BKA, but a pronounced force peak in the lateral direction was elicited by nonamputee athletes during the takeoff step. These results are likely due to differences in mediolateral foot positioning relative to the COM, which are induced and constrained by the mechanical rigidity of the RSP used by athletes with a BKA. Avoiding braking or mediolateral GRF implicates a more efficient takeoff technique. Moreover, lower horizontal GRF and lateral GRF result in lower frontal and transverse joint loading represented by lower hip joint moments or joint work in the respective planes (Fig. 3, Table 1). However, mediolateral force production does not necessarily limit sagittal force application (28) and might provide the opportunity to increase total force output in the sagittal direction by including muscle groups primarily used in other planes of movement, e.g., musculus gluteus medius and minimus or musculus adductor longus, magnus, and brevis. The unique design of RSP may limit the muscle groups available to be used for propulsion and, therefore, could induce a performance limitation for athletes with BKA. Limitations or alterations in mediolateral force production elicited by the use of RSP were also discussed in a case study of an athlete with a unilateral knee disarticular amputation during curve sprinting (21). Future studies of the long jump should investigate whether the differences in mediolateral GRF production between athletes with and without BKA are due to limited force production capacities or result from a fundamentally altered takeoff technique. No sensory feedback is provided by the RSP, which, combined with its set mechanical stiffness, induces a reduced ability to compensate for any undesired movement. This entails the need for greater accuracy during the approach run and might finally result in higher psychological demands and/or more unsuccessful trials compared with nonamputees.

Joint moments and joint work

All of the sagittal plane joint moments of the nonamputee athletes closely matched the results from a previous study (5) with respect to peak values and curve shapes. In addition, the peak ankle dorsiflexion moments of the nonamputee athletes during the takeoff step are similar to those of previous studies on sprinting (12,13). However, the peak external flexion moments at the knee and hip joints of the nonamputee athletes were greater (by a factor of 4 and 1.5) compared with those calculated for nonamputee sprinters in previous studies (12,29). This difference during the long jump takeoff step likely results in higher loads applied on the contracting muscles such as on the musculus biceps femoris, musculus semimembranosus, and musculus semitendinosus of the hip extensors and the musculus quadriceps femoris of the knee extensors. In summary, the hip and especially the knee sagittal plane joint loads were much higher during the takeoff step of the long jump compared with those in sprinting. These results might explain why thigh injuries are the most common among athletes competing in athletic jump disciplines (40%) (20), as the muscle loading results from both knee and hip joint moments. Hip and knee flexion moments of athletes with BKA were smaller (~77% and 55%) compared with nonamputee long jumpers in this and a previous study (5) and were also smaller (~35% and 20%) compared with nonamputee sprinters (12). By contrast, the prosthetic ankle flexion moment was much higher (~200%) in the athletes with BKA compared with the nonamputee long jumpers. This difference is mainly due to the shape of the RSP, which artificially extends the lever arm between the prosthetic ankle joint and the GRF vector compared with a biological foot–ankle complex. The orthogonal distance between the GRF vector and the respective joint center averaged over the duration of ground contact for athletes with BKA was shorter at the hip (−8.5 cm) and knee (−7.7 cm) but longer (+16.6 cm) in the ankle compared with the nonamputees. According to Biewener (30), a “closer alignment of the limb to Fg [GRF vector] increases the muscle’s ‘effective mechanical advantage’ (EMA) at the joint” (p. 46), whereas a further alignment decreases the muscle’s EMA. Furthermore, it appears that athletes with BKA use a strategy to reduce external knee and hip joint moments to maximally load and unload the prosthesis to maximize performance during the takeoff step. They adopt mechanics that increase the load on the carbon fiber prosthesis and decrease the load on the biological tissues at the more proximal nonaffected joints. The mechanism of selective loading and unloading implies that the joint energy changes necessary to prepare the COM to launch at the end of the takeoff step can be provided more effectively with the prosthesis versus the residual limb. A similar strategy was also adopted for sprint running (9.2–9.5 m·s−1) of an athlete with bilateral transtibial amputations (7) and, moreover, serves as a possible explanation for why elite long jumpers with BKA have a more effective takeoff step than nonamputee athletes (6). Moreover, decreasing the load on the biological tissues of the more proximal joints would be beneficial in terms of injury prevention. We did not quantify the extent of cocontraction involved. Conclusions on a possible reduction of muscular fatigue should therefore be drawn with caution and investigations on muscle activity during the long jump takeoff step are needed.

Nonamputee athletes’ peak knee adduction moments were approximately 50% higher than those reported for sprinting at 8.95 ± 0.7 m·s−1 (12) and four to five times higher compared with those reported for activities of daily living, e.g., walking and stair climbing (31,32). A high external knee adduction moment is a surrogate for accelerated progression of medial knee osteoarthritis (18), and the incidence of a high external knee adduction impulse has been linked to patellofemoral pain in runners (19). The knee joints of the athletes with BKA were loaded differently compared with the nonamputee athletes, as shown by differences in timing of flexion/extension and peak joint moments (Fig. 3, Table 1), which are likely due to differences in the magnitude and orientation of the resulting GRF vector (Figs. 2 and 4). In athletes with BKA, the knee joint loading was shifted laterally (mostly abduction moment) compared with the loading applied on the knee joint of nonamputees (mainly adduction moment) during the takeoff step. An external knee abduction moment during the takeoff step for the athletes with BKA (Fig. 3) contrasts with the external knee adduction moments elicited during straight walking (1.3 m·s−1) of people with a unilateral transtibial amputation (33). External knee abduction moments apply load on the lateral knee joint compartment during the takeoff step and, therefore, might stress structures that are not adequately adapted by a daily stimulus from walking. These results are important for athletes and clinicians to differentially diagnose knee pain or injury.

During the first 10% of the stance phase, nonamputee athletes exhibited an external hip abduction moment that has not been shown in previous studies of sprinting (12). Peak hip adduction moments were 2.7-fold higher for nonamputee long jumpers during the takeoff step compared with sprinting at 8.95 m·s−1 (12). The hip abductor muscles, which are important contributors to maintain balance and support body weight (15), therefore, are highly stressed during the takeoff step. However, the role of the hip abductors seems more distinct in nonamputee athletes compared with athletes with BKA. One reason for this could be the absence of considerable mediolateral GRF in athletes with BKA. As more than 60% of the injuries in athletics occur during training and most of them at the beginning of the season (20), athletes should be encouraged to strengthen the muscles surrounding the hip joint before practicing full effort long jump takeoff steps because of the unique loading encountered. The unique loading situation could also lead to asymmetrical muscle atrophy, which could negatively influence posture and result in injuries to more proximal body segments such as the lumbar spine. Thus, to reduce injury, strength training should focus not only on the takeoff leg but also on the nontakeoff leg.

The sagittal plane energy exchange during the takeoff step in all three joints of the nonamputee athletes in this study was higher compared with those reported earlier (4,5). Possible explanations for this are a shorter approach run (4) or different filter protocols for the kinematics with lower cutoff frequencies (5–10 Hz) (4,5). The distribution of joint work within each plane of movement and the comparisons between groups support the findings of Willwacher and colleagues (6) and provide additional insight into the energy absorption and generation/return of biological and mechanical joint structures. Willwacher et al. (6) presented joint work as the sum of all planes of movement and showed an even distribution of joint work between hip, knee, and below knee joints for nonamputee athletes, whereas in athletes with BKA, most of the joint work was absorbed and returned in the prosthesis for the takeoff step. As the takeoff step occurs primarily in the sagittal plane, the sagittal plane joint work presented in the current 3D analysis still closely reflects the results from the previous study (6) where total joint work was presented. Biological limbs have a limited capacity for storing and returning energy in the elastic structures of the lower limb (Achilles tendon, ankle joint ligaments, and extrinsic foot muscles) compared with RSP (6). Therefore, nonamputee athletes are not able to jump with the same mechanics as athletes with BKA who use their affected leg as their takeoff leg but involve muscle–tendon units surrounding the knee and hip joint for storing/absorbing and returning/generating energy (Fig. 5). Moreover, athletes with BKA are not able to jump with the same mechanics of nonamputee athletes because of inherent differences between a prosthesis and a biological limb.

In relation to the respective sagittal plane joint work, both groups elicited considerable work in the frontal plane of the hip joint (25%–216%). However, from an injury prevention or performance perspective, absolute values might be more relevant compared with relative values. Therefore, it should be accented that the frontal and transverse planes of the knee and hip joints have little involvement in absolute energy absorption and generation in athletes with BKA, whereas the hip of nonamputee athletes had high energy changes (Fig. 5, see also Table, Supplemental Digital Content 2, Joint work, https://links.lww.com/MSS/B461), specifically in the frontal plane (absorption, 0.99 J·kg−1; generation/return, 0.87 J·kg−1).

Limitations and perspectives for future research

We were able to recruit a limited number of athletes with BKA, which is due in part to the small number of athletes able to compete at a high performance level. However, we recruited three out of the four best long jumpers with BKA from the 2016 Paralympics. Even with a greater sample size, our findings may not be generalizable and might have overlooked factors, potentially unique to a high performance subgroup of athletes.

All of the joint moments presented in this work are net joint moments and neglect the individual muscular work of the agonist and antagonist. Future studies are needed that use measurements of muscle activation or inverse dynamic approaches, which include muscle models for athletes with BKA. Furthermore, we did not directly elucidate the biomechanical mechanisms of pain and injury during the long jump in this study. Therefore, future studies are needed to confirm our ideas on potential causes of pain and injury in more detail. The calculation of energy absorption and generation is affected by the assumption of two rigid bodies connected by a ball and socket joint. Small deformation of these segments (compression) is neglected by this approach but has been commonly used in biomechanical analyses (7,21,34).

Besides an efficient redirection of the COM velocity during the takeoff step, long jump requires the maximization of controllable run-up speed (1). The steps that are required to accelerate add loads to the musculoskeletal system of the athlete and, thus, sum to the total loading in the long jump but were not included in this analysis because of complexity and space. Neglecting the approach run is an issue because the influence of GRF asymmetry between legs (10,11,35) on joint kinetics, especially in the frontal plane, remains unclear for sprinting and the long jump approach in athletes with a unilateral BKA. Therefore, to more completely determine the musculoskeletal loading during the long jump in athletes with an amputation, future work should also analyze the loading during the approach run.

Athletes with a transfemoral amputation or osseointegrated prosthesis are likely to elicit different long jump takeoff strategies compared with athletes with BKA or nonamputee athletes. Our 3D analysis, however, provides the loads incurred by a prosthesis and, thus, can inform the design of future prostheses. Our results can be used for further analysis, e.g., finite-element-method analysis on the loading capacity of prosthetic components or osseointegrated prosthesis during high-impact sports. These results could also help to address health and safety regulations, specifically whether or not athletes with an osseointegrated prosthesis can participate and/or compete safely in high-impact sports, such as the long jump. Moreover, modeling and simulation have been used to determine control techniques for activities including nonamputee running and sprinting (36,37), sprinting in athletes with BKA (37) and platform diving (38). For complex movements with high loads, such as long jumping, it is important to set realistic model constraints for the underlying mechanics (e.g., peak joint moments) to create realistic and feasible motions and forces.

CONCLUSIONS

We analyzed and compared the 3D GRF and joint loads for athletes with and without BKA during the takeoff step in the long jump. Peak GRF were mostly similar between groups but knee and hip joint loads were lower for athletes with BKA compared with nonamputee athletes. Moreover, the long jump takeoff step of athletes with BKA was dominated by sagittal plane movement, whereas the long jump takeoff step of nonamputees involves additional frontal plane movement. Training protocols and rehabilitation processes should be adapted to the unique loading situations of athletes with or without BKA. Coaches and clinicians should train athletes by strengthening the muscles responsible for hip and knee extension as well as for frontal plane stabilization before these athletes practice the long jump takeoff with full effort. The presented data also enable clinicians to more differentially diagnose potential causes of pain or injuries in the lower extremity joints in both groups of athletes. Future research of the long jump for athletes with unilateral amputation should analyze loads during the approach run for the affected and unaffected legs because musculoskeletal dysfunction and/or injuries can also be caused by overloading the unaffected leg.

Funding was provided by the Japan Broadcasting Cooperation (NHK). J. F. was funded by a graduate fellowship of the German Sport University Cologne. H. H. was funded by JSPS KAKENHI (grant no. 26702027). A. M. G.’s contribution to this project was also partially supported by the BADER Consortium, a U.S. Department of Defense Congressionally Directed Medical Research Programs cooperative agreement (W81XWH-11-2-0222). The authors are grateful to all athletes who participated in the study during a very important training period of an Olympic/Paralympic season. They also thank the technical staff at the German Sport University Cologne and the Japanese Institute of Sport Sciences for their great support and preparations made for the data collections. They thank Denis Holzer, Jana Weichsel, Anna Lena Kleesattel, Erik Schrödter, Stephan Dill, Josef Viellehner, Markus Peters, Igor Komnik, and Markus Kurz for their help during data collection and postprocessing.

None of the authors had any conflict of interest associated with the study. The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The results of the present study do not constitute endorsement by the American College of Sports Medicine.

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Keywords:

JOINT ENERGY; ATHLETICS; FRONTAL PLANE; PROSTHETICS; INJURY PREVENTION; ROBOTICS

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