The mechanical stiffness of running-specific prostheses likely affects the functional abilities of athletes with leg amputations. However, each prosthetic manufacturer recommends prostheses based on subjective stiffness categories rather than performance based metrics. The actual mechanical stiffness values of running-specific prostheses (i.e. kN/m) are unknown. Consequently, we sought to characterize and disseminate the stiffness values of running-specific prostheses so that researchers, clinicians, and athletes can objectively evaluate prosthetic function. We characterized the stiffness values of 55 running-specific prostheses across various models, stiffness categories, and heights using forces and angles representative of those measured from athletes with transtibial amputations during running. Characterizing prosthetic force-displacement profiles with a 2^nd degree polynomial explained 4.4% more of the variance than a linear function (p<0.001). The prosthetic stiffness values of manufacturer recommended stiffness categories varied between prosthetic models (p<0.001). Also, prosthetic stiffness was 10% to 39% less at angles typical of running 3 m/s and 6 m/s (10°-25°) compared to neutral (0°) (p<0.001). Furthermore, prosthetic stiffness was inversely related to height in J-shaped (p<0.001), but not C-shaped, prostheses. Running-specific prostheses should be tested under the demands of the respective activity in order to derive relevant characterizations of stiffness and function. In all, our results indicate that when athletes with leg amputations alter prosthetic model, height, and/or sagittal plane alignment, their prosthetic stiffness profiles also change; therefore variations in comfort, performance, etc. may be indirectly due to altered stiffness.

Purpose: To investigate the effects of an uphill marathon (43 km, 3063-m elevation gain) on running mechanics and neuromuscular fatigue in lower-limb muscles.Methods: Maximal mechanical power of lower limbs (MMP), temporal tensiomyographic (TMG) parameters, and muscle-belly displacement (D_m) were determined in the vastus lateralis muscle before and after the competition in 18 runners (age 42.8 ± 9.9 y, body mass 70.1 ± 7.3 kg, maximal oxygen uptake 55.5 ± 7.5 mL · kg⁻¹ · min⁻¹). Contact (t_c) and aerial (t_a) times, step frequency (f), and running velocity (v) were measured at 3, 14, and 30 km and after the finish line (POST). Peak vertical ground-reaction force (F_max), vertical displacement of the center of mass (Δz), leg-length change (ΔL), and vertical (k_vert) and leg (k_leg) stiffness were calculated.Results: MMP was inversely related with race time (r = –.56, P = .016), t_c (r = –.61, P = .008), and Δz (r = –.57, P = .012) and directly related with F_max (r = .59, P = .010), t_a (r = .48, P = .040), and k_vert (r = .51, P = .027). In the fastest subgroup (n = 9) the following parameters were lower in POST (P < .05) than at km 3: t_a (–14.1% ± 17.8%), F_max (–6.2% ± 6.4%), k_vert (–17.5% ± 17.2%), and k_leg (–11.4% ± 10.9%). The slowest subgroup (n = 9) showed changes (P < .05) at km 30 and POST in F_max (–5.5% ± 4.9% and –5.3% ± 4.1%), t_a (–20.5% ± 16.2% and –21.5% ± 14.4%), t_c (5.5% ± 7.5% and 3.2% ± 5.2%), k_vert (–14.0% ± 12.8% and –11.8% ± 10.0%), and k_leg (–8.9% ± 11.5% and –11.9% ± 12%). TMG temporal parameters decreased in all runners (–27.35% ± 18.0%, P < .001), while D_m increased (24.0% ± 35.0%, P = .005), showing lower-limb stiffness and higher muscle sensibility to the electrical stimulus.Conclusions: Greater MMP was related with smaller changes in running mechanics induced by fatigue. Thus, lower-limb power training could improve running performance in uphill marathons.

The aim of the present study was to evaluate the effects of a 12‐week home‐based strength, explosive and plyometric (SEP) training on the cost of running (Cr) in well‐trained ultra‐marathoners and to assess the main mechanical parameters affecting changes in Cr. Twenty‐five male runners (38.2 ± 7.1 years; body mass index: 23.0 ± 1.1 kg·m⁻²; V˙O₂max: 55.4 ± 4.0 mlO₂·kg⁻¹·min⁻¹) were divided into an exercise (EG = 13) and control group (CG = 12). Before and after a 12‐week SEP training, Cr, spring‐mass model parameters at four speeds (8, 10, 12, 14 km·h⁻¹) were calculated and maximal muscle power (MMP) of the lower limbs was measured. In EG, Cr decreased significantly (p < .05) at all tested running speeds (−6.4 ± 6.5% at 8 km·h⁻¹; −3.5 ± 5.3% at 10 km·h⁻¹; −4.0 ± 5.5% at 12 km·h⁻¹; −3.2 ± 4.5% at 14 km·h⁻¹), contact time (t_c) increased at 8, 10 and 12 km·h⁻¹ by mean +4.4 ± 0.1% and t_a decreased by −25.6 ± 0.1% at 8 km·h⁻¹ (p < .05). Further, inverse relationships between changes in Cr and MMP at 10 (p = .013; r = −0.67) and 12 km·h⁻¹ (p < .001; r = −0.86) were shown. Conversely, no differences were detected in the CG in any of the studied parameters. Thus, 12‐week SEP training programme lower the Cr in well‐trained ultra‐marathoners at submaximal speeds. Increased t_c and an inverse relationship between changes in Cr and changes in MMP could be in part explain the decreased Cr. Thus, adding at least three sessions per week of SEP exercises in the normal endurance‐training programme may decrease the Cr.

Purpose: To investigate the effects of an extreme uphill marathon on the mechanical parameters that are likely to affect the energy cost of running (Cr).Methods: Eleven runners (27–59 y) participated in the Etna SuperMarathon (43 km, 0–3063 m above sea level). Anthropometric characteristics, maximal explosive power of the lower limb (P_max), and maximal oxygen uptake were determined before the competition. In addition, before and immediately after the race, Cr, contact (t_c) and aerial (t_a) times, step frequency (f), and running velocity were measured at constant self-selected speed. Then, peak vertical ground-reaction force (F_max), vertical downward displacement of the center of mass (Δz), leg-length change (ΔL), and vertical (k_vert) and leg (k_leg) stiffness were calculated.Results: A direct relationship between Cr, measured before the race, and race time was shown (r = .61, P < .001). Cr increased significantly at the end of the race by 8.7%. Immediately after the race, the subjects showed significantly lower t_a (–58.6%), f (–11.3%), F_max (–17.6%), k_vert (–45.6%), and k_leg (–42.3%) and higher t_c (+28.6%), Δz (+52.9%), and ΔL (+44.5%) than before the race. The increase of Cr was associated with a decrement in F_max (r = –.45), k_vert (r = –.44), and k_leg (r = –.51). Finally, an inverse relationship between P_max measured before the race and ΔCr during race was found (r = –.52).Conclusions: Lower Cr was related with better performance, and athletes characterized by the greater P_max showed lower increases in Cr during the race. This suggests that specific power training of the lower limbs may lead to better performance in ultraendurance running competition.

Historically, several different approaches have been applied to explain the metabolic cost of uphill human running. Most of these approaches result in unrealistically high values for the efficiency of performing vertical work during running uphill, or are only valid for running up steep inclines. The purpose of this study was to reexamine the metabolic cost of uphill running, based upon our understanding of level running energetics and ground reaction forces during uphill running. In contrast to the vertical efficiency approach, we propose that during incline running at a certain velocity, the forces (and hence metabolic energy) required for braking and propelling the body mass parallel to the running surface are less than during level running. Based on this idea, we propose that the metabolic rate during uphill running can be predicted by a model, which posits that (1) the metabolic cost of perpendicular bouncing remains the same as during level running, (2) the metabolic cost of running parallel to the running surface decreases with incline, (3) the delta efficiency of producing mechanical power to lift the COM vertically is constant, independent of incline and running velocity, and (4) the costs of leg and arm swing do not change with incline. To test this approach, we collected ground reaction force (GRF) data for eight runners who ran thirty 30-second trials (velocity: 2.0-3.0 m/s; incline: 0-9°). We also measured the metabolic rates of eight different runners for 17, 7-minute trials (velocity: 2.0-3.0 m/s; incline: 0-8°). During uphill running, parallel braking GRF approached zero for the 9° incline trials. Thus, we modeled the metabolic cost of parallel running as exponentially decreasing with incline. With that assumption, best-fit parameters for the metabolic rate data indicate that the efficiency of producing mechanical power to lift the center of mass vertically was independent of incline and running velocity, with a value of ∼29%. The metabolic cost of uphill running is not simply equal to the sum of the cost of level running and the cost of performing work to lift the body mass against gravity. Rather, it reflects a constant cost of perpendicular bouncing, decreased costs of parallel braking and propulsion and of course the cost of lifting body mass against gravity.