Hiroaki Hobara

Amputee locomotion: Spring-like leg behavior and stiffness regulation using running-specific prostheses

Carbon fiber running-specific prostheses (RSPs) have allowed individuals with lower extremity amputation (ILEA) to participate in running. It has been established that as running speed increases, leg stiffness (Kleg) remains constant while vertical stiffness (Kvert) increases in able-bodied runners. The Kvert further depends on a combination of the torsional stiffnesses of the joints (joint stiffness; Kjoint) and the touchdown joint angles. Thus, an increased understanding of spring-like leg function and stiffness regulation in ILEA runners using RSPs is expected to aid in prosthetic design and rehabilitation strategies. The aim of this study was to investigate stiffness regulation to various overground running speeds in ILEA wearing RSPs. Eight ILEA performed overground running at a range of running speeds. Kleg, Kvert and Kjoint were calculated from kinetic and kinematic data in both the intact and prosthetic limbs. Kleg and Kvert in both the limbs remained constant when running speed increased, while intact limbs in ILEA running with RSPs have a higher Kleg and Kvert than residual limbs. There were no significant differences in Kankle, Kknee and touchdown knee angle between the legs at all running speeds. Hip joints in both the legs did not demonstrate spring-like function; however, distinct impact peaks were observed only in the intact leg hip extension moment at the early stance phase, indicating that differences in Kvert between limbs in ILEA are due to attenuating shock with the hip joint. Therefore, these results suggest that ILEA using RSPs has a different stiffness regulation between the intact and prosthetic limbs during running.

A comparison of computation methods for leg stiffness during hopping.

Despite the presence of several different calculations of leg stiffness during hopping, little is known about how the methodologies produce differences in the leg stiffness. The purpose of this study was to directly compare Kleg during hopping as calculated from three previously published computation methods. Ten male subjects hopped in place on two legs, at four frequencies (2.2, 2.6, 3.0, and 3.4 Hz). In this article, leg stiffness was calculated from the natural frequency of oscillation (method A), the ratio of maximal ground reaction force (GRF) to peak center of mass displacement at the middle of the stance phase (method B), and an approximation based on sine-wave GRF modeling (method C). We found that leg stiffness in all methods increased with an increase in hopping frequency, but Kleg values using methods A and B were significantly higher than when using method C at all hopping frequencies. Therefore, care should be taken when comparing leg stiffness obtained by method C with those calculated by other methods.

Key joint kinematic characteristics of the gait of fallers identified by principal component analysis.

It has been reported that fallers have a higher risk of subsequent falls than non-fallers. Therefore, if the differences between the movements of recent fallers and non-fallers can be identified, such could be regarded as the basis of the high risk of falling of the former. The objective of the present study was the identification of the key joint kinematic characteristics of human gait related to the risk of falling while walking on level ground. For this purpose, joint kinematics data obtained from 18 recent fallers and 19 non-fallers were analyzed using principal component analysis (PCA). The PCA was conducted using an input matrix constructed from the time-normalized average and standard deviation of the lower limb joint angles on three planes (101 data×2 parameters×3 angles×3 planes). The PCA revealed that only the 5th principal component vector (PCV 5) among the 23 generated PCVs was related to the risk of falling (p<0.05, ES=0.71). These findings as well as those of previous studies suggest that the joint kinematics of PCV 5 is the key characteristic that affects the risk of falling while walking. We therefore recombined the joint kinematics corresponding to PCV 5 and concluded that the variability of the joint kinematics for fallers was larger than that for non-fallers regardless of the joint. These observations as well as the findings of previous studies suggest that the risk of falling can be reduced by reducing the variability of the joint kinematics using an intervention such as external cues or a special garment.

Amputee locomotion: Lower extremity loading using running-specific prostheses

Carbon fiber running-specific prostheses (RSPs) have allowed individuals with lower extremity amputation (ILEA) to actively participate in sporting activities including competitive sports. In spite of this positive trait, the RSPs have not been thoroughly evaluated regarding potential injury risks due to abnormal loading during running. Vertical impact peak (VIP) and average loading rate (VALR) of the vertical ground reaction force (vGRF) have been associated with running injuries in able-bodied runners but not for ILEA. The purpose of this study was to investigate vGRF loading in ILEA runners using RSPs across a range of running speeds. Eight ILEA with unilateral transtibial amputations and eight control subjects performed overground running at three speeds (2.5, 3.0, and 3.5m/s). From vGRF, we determined VIP and VALR, which was defined as the change in force divided by the time of the interval between 20 and 80% of the VIP. We observed that VIP and VALR increased in both ILEA and control limbs with an increase in running speed. Further, the VIP and VALR in ILEA intact limbs were significantly greater than ILEA prosthetic limbs and control subject limbs for this range of running speeds. These results suggest that (1) loading variables increase with running speed not only in able-bodied runners, but also in ILEA using RSPs, and (2) the intact limb in ILEA may be exposed to a greater risk of running related injury than the prosthetic limb or able-bodied limbs.

Spatiotemporal Variables of Able-bodied and Amputee Sprinters in Men’s 100-m Sprint

The difference in world records set by able-bodied sprinters and amputee sprinters in the mens 100-m sprint is still approximately 1 s (as of 28 March 2014). Theoretically, forward velocity in a 100-m sprint is the product of step frequency and step length. The goal of this study was to examine the hypothesis that differences in the sprint performance of able-bodied and amputee sprinters would be due to a shorter step length rather than lower step frequency. Mens elite-level 100-m races with a total of 36 able-bodied, 25 unilateral and 17 bilateral amputee sprinters were analyzed from the publicly available internet broadcasts of 11 races. For each run of each sprinter, the average forward velocity, step frequency and step length over the whole 100-m distance were analyzed. The average forward velocity of able-bodied sprinters was faster than that of the other 2 groups, but there was no significant difference in average step frequency among the 3 groups. However, the average step length of able-bodied sprinters was significantly longer than that of the other 2 groups. These results suggest that the differences in sprint performance between 2 groups would be due to a shorter step length rather than lower step frequency.

Lower extremity joint kinematics of stair ascent in transfemoral amputees.

Background: Stair ascent is a very demanding task for transfemoral amputees (TFAs). The purpose of this study was to investigate the lower extremity joint kinematics of TFAs who can climb stairs using a step-over-step gait pattern without an active artificial prosthetic knee joint or handrail use. Case Description and Methods: Case series. Participants were two traumatic TFAs and 10 control participants. Both TFAs used a single-axis prosthetic knee joint in daily living. Sagittal plane joint kinematics were recorded at 60 Hz using an eight-camera motion analysis system and digital video camera. Findings and Outcomes: From the instant of touchdown, the prosthetic knee joint was rapidly extended and remained fully extended until toe-off. In the latter half of the stance phase, the knee and ankle joints of the sound limb simultaneously showed rapid joint flexion during continuous extension. Further, the ankle joint of the sound limb showed greater plantarflexion at the end of the stance phase. Conclusion: These results suggest that the TFA in the present study would (1) extend the prosthetic knee joint to prevent the knee flexion generated by the bodyweight (plus ground reaction force and/or joint moment), and (2) lift the whole body in an upward direction using strong counter-movements and greater joint extension during the stance phase.

Normative Spatiotemporal Parameters During 100-m Sprints in Amputee Sprinters Using Running-Specific Prostheses

The aim of this study was to develop a normative sample of step frequency and step length during maximal sprinting in amputee sprinters. We analyzed elite-level 100-m races of 255 amputees and 93 able-bodied sprinters, both men and women, from publicly-available Internet broadcasts. For each sprinters run, the average forward velocity, step frequency, and step length over the 100-m distance were analyzed by using the official record and number of steps in each race. The average forward velocity was greatest in able-bodied sprinters (10.04 ± 0.17 m/s), followed by bilateral transtibial (8.77 ± 0.27 m/s), unilateral transtibial (8.65 ± 0.30 m/s), and transfemoral amputee sprinters (7.65 ± 0.38 m/s) in men. Differences in velocity among 4 groups were associated with step length (able-bodied vs transtibial amputees) or both step frequency and step length (able-bodied vs transfemoral amputees). Although we also found that the velocity was greatest in able-bodied sprinters (9.10 ± 0.14 m/s), followed by unilateral transtibial (7.08 ± 0.26 m/s), bilateral transtibial (7.06 ± 0.48 m/s), and transfemoral amputee sprinters (5.92 ± 0.33 m/s) in women, the differences in the velocity among the groups were associated with both step frequency and step length. Current results suggest that spatiotemporal parameters during a 100-m race of amputee sprinters is varied by amputation levels and sex.

Leg stiffness and sprint ability in amputee sprinters

Background: Understanding leg stiffness (Kleg) in amputee sprinters is important for the evaluation of their sprint ability and development of running-specific prostheses (RSP). Objectives: To investigate Kleg during hopping in amputee sprinters. Study Design: Cross-sectional study. Methods: Seven transtibial (TT) and seven transfemoral (TF) amputee sprinters, as well as seven non-active able-bodied subjects, performed one-legged hopping matching metronome beats at 2.2 Hz. Amputees hopped on their sound limb whereas able-bodied (AB) subjects hopped on their dominant limb. Using a spring-mass model, Kleg was calculated from the subjects’ body mass, ground contact and flight times. Results: Both TT and TF sprinters demonstrated significantly higher Kleg than AB subjects. Kleg during hopping on the sound leg significantly correlated with personal records attained in a 100-m sprint in both TT (r = −0.757) and TF sprinters (r = −0.855). Conclusion: The results of the present study suggest that amputee sprinters have a greater Kleg during hopping than inactive non-amputees, and that their sprint ability can be predicted from the Kleg during hopping at 2.2 Hz on the sound limb. Clinical relevance Exercise challenges need to be taken into consideration when planning routine training regimens for amputee sprinters. Furthermore, increased understanding of Kleg in amputee sprinters is relevant to evaluate their sprint ability and develop running-specific prostheses.

The fastest sprinter in 2068 has an artificial limb

Recent developments in carbon fiber running-specific prostheses (RSPs) with energy-storing capabilities have allowed individuals with lower extremity amputation (ILEAs) to regain the ability to run. This phenomenon exemplifies how ILEA sprinters are highly motivated and work hard as well as how current prostheses have advanced. This raises the following question: How fast would RSPs allow ILEA sprinters to run? Although several studies predicted limitations in sprint performance in able-bodied sprinters (ABSs),1,2 no studies have been reported for ILEA sprinters. We assessed the progression of the winning times of the men’s 100-m sprint in the Paralympics and compared them with those in the Olympics. The winning times of the men’s 100-m sprint in the Olympics were obtained from the official website of the Olympic Movement (http://www.olympic.org/). Data were available every 4 years from 1900 to 2012 except for 1912–1920 and 1936–1948 when the Olympic Games were cancelled due to World Wars I and II, respectively. We also acquired data for the winning times at the Paralympics from the official website of the Paralympic Movement (http://www.paralympic.org/). Data were available every 4 years from 1976 to 2012. In this study, we included the winning times of the men’s 100-m sprint in the C (1976 and 1980), A4 (1984), A4-A9 (1988), TS2 (1992), T43-44 (1996), and T44 (2000, 2004, 2008, and 2012) classifications. We performed regression analyses to predict the winning time for future Olympics and Paralympics for ABS and ILEA sprinters, respectively. Since the carbon fiber prosthesis was first seen in elite sporting events at the 1988 Paralympic Games,3 data for ILEA sprinters in 1976, 1980, and 1984 were excluded from the regression analyses. The 95% confidence intervals on the predicted winning times were also calculated in the analyses. The significance was set at p < 0.01 in each regression analysis. The difference in winning times between ABSs and ILEAs was over 4 s in 1976 (Figure 1). The ILEAs shaved approximately 1.5 s off the time difference from 1984 to 1988. This improvement may be attributed to the advent of carbon fiber prosthetic feet at the 1988 Paralympic Games.3 These results suggest that technological interventions, such as the advent of RSPs, would contribute to the improvement of the sprint performance of ILEAs. In other words, revolutionary new materials or technical advances may induce drastic performance improvements in the future, similar to that seen from 1984 to 1988. As of 2012, the difference between the two groups has gone down to 1.27 s. The current world records (as of 29 September 2014) are 9.58 s for ABS and 10.57 s for ILEAs, which represent a difference that is already less than 1 s. Our regression model predicted that ILEA sprinters would outperform ABS in 2068, where the predicted winning times could be 9.039 and 9.046 s, respectively. These results indicate that if current trends continue, the fastest sprinters in the world may be ILEAs from 2068 onward.

Step Frequency and Step Length of 200-m Sprint in Able-bodied and Amputee Sprinters

The goal of this study was to examine the hypothesis that the difference in the 200-m sprint performance of amputee and able-bodied sprinters is due to a shorter step length rather than a lower step frequency. Mens elite-level 200-m races with a total of 16 able-bodied, 13 unilateral transtibial, 5 bilateral transtibial, and 16 unilateral transfemoral amputee sprinters were analyzed from publicly available internet broadcasts. For each run, the average forward velocity, step frequency, and step length over the entire 200-m distance were analyzed for each sprinter. The average forward velocity of able-bodied sprinters was faster than that of the other 3 groups, but there was no significant difference in average step frequency between able-bodied and transtibial amputee sprinters. However, the average step length of able-bodied sprinters was significantly longer than that of the transtibial amputee sprinters. In contrast, the step frequency and step length of transfemoral amputees were significantly lower and shorter than those of the other 3 groups. These results suggest that the differences in 200-m sprint performance between able-bodied and amputee sprinters are dependent on amputation level.