ENERGETICS AND MECHANICS OF RUNNING: THE INFLUENCE OF BODY MASS AND THE USE OF RUNNING SPECIFIC PROSTHESES

The first measurements on running humans date back since the beginning of 20th century. However, most of the studies were focused on ordinary/average subjects. To better understand how body characteristics influence the biomechanics and the energetics of running, extra-ordinary subjects and athletes need to be involved. This thesis will be divided in two main parts: the first part will focus on the influence of body mass on the energetics and biomechanics of running; the second part will focus on the use of running specific prostheses in sprint running. PART I. In the first part we investigated the relationship between mechanical and energy cost of transport and body mass in running humans. Ten severely obese (body mass ranging from 108.5 to 172.0 kg) and 15 normal-weighted (52.0–89.0 kg) boys and men, aged 16.0–45.8 years, participated in this study. The rate of O2 consumption was measured and the subjects were filmed with four cameras for kinematic analysis, while running on a treadmill at 8 km•h-1. Mass specific energy cost (Cr) and external mechanical work (Wext) per unit distance were calculated and expressed in joules per kilogram per meter, efficiency (η) was then calculated as Wext × Cr-1 × 100. Both mass-specific Cr and Wext were found to be independent of body mass (M) (Cr = 0.002 M + 3.729, n = 25, R2 = 0.05; Wext = -0.001 M + 1.963, n = 25, R2 = 0.01). It necessarily follows that the efficiency is also independent of M (η = -0.062 M + 53.3298, n = 25, R2 = 0.05). The results strongly suggest that the elastic tissues of obese subjects can adapt (e.g., thickening) to the increased mass of the body thus maintaining their ability to store elastic energy, at least at 8 km•h-1speed, at the same level as the normal-weighted subjects. PART II. In the second part we investigated two aspects of sprint running: the start, in particular starting blocks configurations, and curve running. Part IIa: The aim of the present study was to measure the effect of starting block configuration on starting performance of both non-amputee sprinters and athletes with unilateral transtibial amputations. A total of 16 subjects participated in this study: 7 (6 males and 1 female) were non-amputee sprinters and 9 (7 males and 2 females) were sprinters with a unilateral transtibial amputation. Each subject performed a total of 6 starts, alternating between their usual and unusual starting block configurations, on two separate force platforms located underneath a runway covered with a rubber mat, which allowed each athlete to use their own spiked shoes. For each amputee sprinter, we used data from their unaffected leg (UL) and affected leg (AL) to simulate their start mechanics as if they had two unaffected legs (“a virtual non-amputee”) or had two affected legs (“a virtual bilateral amputee”). Non-amputee sprinters had better horizontal acceleration, and therefore overall better starts, in their usual configuration (7.63 ± 0.91 vs. 7.39 ± 0.84 m∙s-2, p=0.042, n=7). When amputees put their UL on the front block, they developed 6% greater mean resultant forces (1.38 ± 0.06 vs. 1.30 ± 0.11 BW, p=0.015, n=9). However, in contrast with our hypothesis, horizontal acceleration was not statistically different between the UL and AL in front configurations. Virtual bilateral amputee sprinters had worse start performance compared to virtual non-amputees: a 21% smaller resultant force and a 6% more vertical push-angle (although not statistically different), which resulted in a 23% slower horizontal acceleration. These results support the impression that, among similar-level athletes (i.e. same overall times), bilateral amputees have slower starts than unilateral amputees, and unilateral amputees have slower starts than non-amputees. Part IIb: The first objective of this study was to compare curve running performance between non-amputee sprinters and sprinters with unilateral transtibial amputations. We hypothesized that athletes with and without unilateral transtibial amputations would be slower during maximal speed curve running compared to maximal speed straight running. Given that the inside leg is thought to limit curve running speed, we hypothesized that sprinters with a unilateral leg amputation would be slower in curves with their affected leg on the inside of the curve, compared to curves with their affected leg on the outside of the curve. A total of 14 subjects participated: 6 (5M/1F) non-amputee sprinters, 6 (5M/1F) sprinters with a right leg transtibial amputation, and 2 (1M/1F) sprinters with a left leg transtibial amputation. Each subject performed a total of six 40 m sprints on a standard synthetic track surface, wearing their own spiked shoes. The curve of the track was not banked and had a radius of 17.2 m. Each subject performed two sprints in a straight direction (S), two on a clockwise (CW) curve and two on a counterclockwise (CCW) curve. We used a high-speed video camera with a frame-rate of 210 fps to record each subject during each trial. Non-amputee sprinters ran the last 20 m of the straight running trials faster (8.05 ± 0.65 m•s-1) compared to the counterclockwise (7.39 ± 0.49 m•s-1) and clockwise (7.25 ± 0.45 m•s-1) curves (p=0.002 and p=0.001 respectively). All of the sprinters with leg amputations ran faster during the straight trials (7.82 ± 0.63 m•s-1), compared to curve running with their affected leg on the outside (7.43 ± 0.56 m•s-1) and curve running with their affected leg on the inside (7.05 ± 0.51 m•s-1) (p=0.001 for both comparisons). For sprinters with leg amputations, we found that during curve running with the affected leg on the outside the velocities were 4.9% higher, on average, compared to curve running with the affected leg on the inside. This confirms our second hypothesis: the maximum running velocity on curves is limited by the affected leg.