Ine Van Caekenberghe

Mechanics of overground accelerated running vs. running on an accelerated treadmill

Unsteady state gait involving net accelerations has been studied overground and on a treadmill. Yet it has never been tested if and to what extent both set-ups are mechanically equal. This study documents the differences in ground reaction forces for accelerated running on an instrumented runway and running on an accelerating treadmill by building a theoretical framework which is experimentally put to the test. It is demonstrated that, in contrast to overground, no mean fore-after force impulse should be generated to follow an accelerating treadmill due to the absence of linear whole body acceleration. Accordingly, the adaptations in the braking phase (less braking) and propulsive phase (more propulsion) to accelerate overground are not present to follow an accelerating treadmill. It can be concluded that running on an accelerating treadmill is mechanically different from accelerated running overground.

Joint kinematics and kinetics of overground accelerated running versus running on an accelerated treadmill

Literature shows that running on an accelerated motorized treadmill is mechanically different from accelerated running overground. Overground, the subject has to enlarge the net anterior–posterior force impulse proportional to acceleration in order to overcome linear whole body inertia, whereas on a treadmill, this force impulse remains zero, regardless of belt acceleration. Therefore, it can be expected that changes in kinematics and joint kinetics of the human body also are proportional to acceleration overground, whereas no changes according to belt acceleration are expected on a treadmill. This study documents kinematics and joint kinetics of accelerated running overground and running on an accelerated motorized treadmill belt for 10 young healthy subjects. When accelerating overground, ground reaction forces are characterized by less braking and more propulsion, generating a more forward-oriented ground reaction force vector and a more forwardly inclined body compared with steady-state running. This change in body orientation as such is partly responsible for the changed force direction. Besides this, more pronounced hip and knee flexion at initial contact, a larger hip extension velocity, smaller knee flexion velocity and smaller initial plantarflexion velocity are associated with less braking. A larger knee extension and plantarflexion velocity result in larger propulsion. Altogether, during stance, joint moments are not significantly influenced by acceleration overground. Therefore, we suggest that the overall behaviour of the musculoskeletal system (in terms of kinematics and joint moments) during acceleration at a certain speed remains essentially identical to steady-state running at the same speed, yet acting in a different orientation. However, because acceleration implies extra mechanical work to increase the running speed, muscular effort done (in terms of power output) must be larger. This is confirmed by larger joint power generation at the level of the hip and lower power absorption at the knee as the result of subtle differences in joint velocity. On a treadmill, ground reaction forces are not influenced by acceleration and, compared with overground, virtually no kinesiological adaptations to an accelerating belt are observed. Consequently, adaptations to acceleration during running differ from treadmill to overground and should be studied in the condition of interest.

Biomechanics of spontaneous overground walk-to-run transition

SUMMARY The purpose of the present study was to describe the biomechanics of spontaneous walk-to-run transitions (WRTs) in humans. After minimal instructions, 17 physically active subjects performed WRTs on an instrumented runway, enabling measurement of speed, acceleration, spatiotemporal variables, ground reaction forces and 3D kinematics. The present study describes (1) the mechanical energy fluctuations of the body centre-of-mass (BCOM) as a reflection of the whole-body dynamics and (2) the joint kinematics and kinetics. Consistent with previous research, the spatiotemporal variables showed a sudden switch from walking to running in one transition step. During this step there was a sudden increase in forward speed, the so-called speed jump (0.42 m s−1). At total body level, this was reflected in a sudden increase in energy of the BCOM (0.83±0.14 J kg−1) and an abrupt change from an out-of-phase to an in-phase organization of the kinetic and potential energy fluctuations. During the transition step a larger net propulsive impulse compared with the preceding and following steps was observed due to a decrease in the braking impulse. This suggests that the altered landing configuration (prepared during the last 40% of the preceding swing) places the body in an optimal configuration to minimize this braking impulse. We hypothesize this configuration also evokes a reflex allowing a more powerful push off, which generates enough power to complete the transition and launch the first flight phase. This powerful push-off was also reflected in the vertical ground reaction force, which suddenly changed to a running pattern.

Initial foot contact and related kinematics affect impact loading rate in running

ABSTRACT This study assessed kinematic differences between different foot strike patterns and their relationship with peak vertical instantaneous loading rate (VILR) of the ground reaction force (GRF). Fifty-two runners ran at 3.2 m · s−1 while we recorded GRF and lower limb kinematics and determined foot strike pattern: Typical or Atypical rearfoot strike (RFS), midfoot strike (MFS) of forefoot strike (FFS). Typical RFS had longer contact times and a lower leg stiffness than Atypical RFS and MFS. Typical RFS showed a dorsiflexed ankle (7.2 ± 3.5°) and positive foot angle (20.4 ± 4.8°) at initial contact while MFS showed a plantar flexed ankle (−10.4 ± 6.3°) and more horizontal foot (1.6 ± 3.1°). Atypical RFS showed a plantar flexed ankle (−3.1 ± 4.4°) and a small foot angle (7.0 ± 5.1°) at initial contact and had the highest VILR. For the RFS (Typical and Atypical RFS), foot angle at initial contact showed the highest correlation with VILR (r = −0.68). The observed higher VILR in Atypical RFS could be related to both ankle and foot kinematics and global running style that indicate a limited use of known kinematic impact absorbing “strategies” such as initial ankle dorsiflexion in MFS or initial ankle plantar flexion in Typical RFS.

Striking the ground with a neutral ankle angle results in higher impacts in distance running

Driscoll, H. F., Kelly, J., Kirk, B., Koerger, H., & Haake, S. (2015). Measurement of studded shoe–surface interaction metrics during in situ performance analysis. Sports Engineering, 18(2), 105–113. Neto, O. P., Silva, J. H., de Miranda Marzullo, A. C., Bolander, R. P., & Bir, C. A. (2012). The effect of hand dominance on martial arts strikes. Human Movement Science, 31(4), 824– 828. Oudshoorn, B. Y., Driscoll, H. F., Dunn, M., & James, D. (2016). Procedia Engineering, 147, 496–500. Ura, D., & Carr e, M. (2016). Procedia Engineering, 147, 550– 555.

DOES FOOT PRONATION CAUSES VASCULAR CONSTRICTION

Background The most popular hypothesis of the etiology of Achilles tendinopathy suggests that excessive pronation causes conflicting rotational motions, leading to a vascular constriction of the Achilles tendon, described as the “whipping phenomenon” (Clement et al., 1984). Although several studies identified pronation as a risk factor for the development of Achilles tendinopathy, the hypothesis that foot pronation causes vascular constriction of the tendon has not been investigated. Objective Therefore, the aim of this study was to investigate whether the amount of pronation during running influences the Achilles tendon blood flow. Design Cross-sectional study. Setting Runners Service Lab, Zwijndrecht, Belgium. Patients (or Participants) Twenty-five experienced runners (average running time 6.1±2.4 hours/week) aged 34.5±10.2 years participated in this study. Interventions (or Assessment of Risk Factors) 2D-lower limb kinematics during barefoot and shod running in both frontal and sagittal plane were assessed. Blood flow of the Achilles tendon was measured before and after barefoot and shod running, by use of the oxygen-to-see device. Main Outcome Measurements The increase of blood flow after running was registered as outcome variable. Mixed models analyses were executed with kinematic variables as fixed predictors. Results The results of this study confirm that the more pronation excursion during running, the lower the increase in blood flow after running in both insertion and midportion (p=0.085 and 0.037, respectively). In addition, this study revealed that a higher average pronation velocity indicates a lower increase in blood flow after running at insertion (p=0.044). Next, this study also showed that the dorsiflexion excursion or the foot strike pattern was not correlated with blood flow after running. Conclusions We can conclude that our findings indicate that foot pronation causes vascular constriction of the Achilles tendon, and therefore support this aspect of the whipping phenomenon.

Kinematic differences between (a)typical initial rearfoot and midfoot contact patterns

Introduction One of the most common ways to classify running style is by describing the initial foot contact pattern (IFCP). Based on the first contact with the ground, IFCPs can be categorized as initial rearfoot (IRFC), midfoot (IMFC) or forefoot (IFFC) contact. In shod distance running approximately 75% of runners show an IRFC, 20% an IMFC and 5% an IFFC (Breine et al. 2014, Hasegawa et al. 2007). The IFCP is related to the initial foot position, but also to the foot unroll kinematics (Pohl et al. 2008). In a recent study (Breine et al. 2014) we have found that of the registered IRFC contacts, 44% showed atypical center of pressure (COP) patterns. Although these contacts showed an initial COP at the rear 1/3 of the foot (IRFC), they were named atypical IRFC (aIRFC) because the first contact is followed by an initial fast anterior COP displacement at the lateral shoe margin towards the midfoot zone with an early first metatarsal contact after which the COP moves medially into the midfoot zone, similar to IMFC. The fast initial COP movement into the midfoot region in aIRFC seems only feasible with a ‘flatter’ initial foot position. As such, we hypothesize that aIRFC show a ‘flatter’ initial foot position which also resembles to an IMFC. The relevance of discerning the aIRFC can be found in the observed higher instantaneous vertical loading rates of the GRF (VILR) in the aIRFC compared to the other IFCP, which suggests an increased risk for impact related injuries. Purpose of the study The purpose of this study was to assess the kinematic differences between aIRFC, Typical IRFC (tIRFC) and IMFC/IFFC runners. We hypothesized that an aIRFC resembles kinematically most to an IMFC.

Ageing effects on functional phases of the foot unroll during walking

The results of this study indicate that LBS at the MPJ systematically alters the GRF lever arms acting about the ankle joint. In principle, longer lever arms of the GRF give the potential for counteracting muscle tendon units (MTUs) to produce higher propulsive joint moments. Still, individual response data indicates that not all subjects were able to use this higher potential to increase AJMs, but rather produced decreased AJMs during a longer push-off time. Reasons for this might be found in lower force generation capacities of plantarflexing MTUs in these runners. The relationship between alterations in AJM, ankle lever arm and push-off time might be used to determine optimum stiffness values for a given individual. The fact that lever arms were less affected at the knee and hip joints implies that further adaptations of the individual locomotion pattern (e.g. forward leaning) must have been present.

A gradual shift in initial foot-to-ground contact patterns depending upon acceleration

Introduction Running involving sub-maximal accelerations occurs very frequently during sports. Insight into the biomechanics of this type of unsteady locomotion therefore is of interest for e.g. footwear design and sports training. A net acceleration of the body centre of mass (BCOM) is realized by increasing the net horizontal impulse by proportionally less braking and more propulsion (Van Caekenberghe et al., in press), while controlling total body angular momentum. The increase in net impulse is related to a more anterior ground reaction force (GRF) vector and is accompanied in kinematics by an equally more forward body lean (Kugler and Janshen, 2010). Body lean is quantified as the angle relative to the vertical of a line between the BCOM and the centre of pressure (COP) which can be regarded as a moving pivot-point mechanism, among others determined by its initial contact location on the foot. Maximal accelerations during sprinting are characterized by an active (clawing) touchdown on the forefoot (Johnson and Buckley, 2001). Given the gradual change in force characteristics and body orientation, a gradual change in foot fall patterns towards the touchdown observed during maximal accelerations is expected during sub-maximal accelerations. The location of initial foot to ground contact is hypothesized to shift anteriorly on the foot (change towards forefoot strike (FFS)) with larger accelerations. However, at steady state, interindividual differences in the location of initial foot contact (already) exist. Rearfoot strikers (RFS) have a larger margin of progression to the FFS pattern than midfootstrikers (MFS), as such a larger acceleration effect is expected in the RFS population. Another means of quantifying initial foot contact consists in the foot-toground angle at initial contact, which is hypothesized to enlarge (i.e. toes gradually lower than the heel) as acceleration enlarges.