The influence of boot longitudinal flexural stiffness on external mechanical work and running economy during skate roller-skiing: A case study

This case study examines the impact of boot longitudinal flexural stiffness on the total external mechanical work of a skier’s centre of mass per distance travelled in the forward direction ([Formula: see text] EX (J/m)) and on running economy during skate roller-skiing under submaximal steady-state conditions. Moreover, it analyses time derivatives of total W EX, of W EX performed by the roller-skis and poles, respectively, and of the directly useful mechanical work (the sum of the work to overcome centre of mass’ gravity and rolling resistance) within a typical roller-skiing cycle. Multiple roller-skiing trials (G3 technique) were performed by one subject on an inclined treadmill with boots of soft, intermediate, and stiff flexural stiffness. The orientation and magnitude of the roller-ski and pole ground reaction forces, body kinematics, VO2, and lactic acid concentration were monitored. The stiff boots had 13.4% ( p < 0.01) lower [Formula: see text] EX compared to the intermediate boots, and 20.7% ( p < 0.001) lower [Formula: see text] EX compared to the soft boots. Regarding running economy, the soft boots had 2.2% ( p < 0.05) higher VO2 compared to the intermediate boots, but the same VO2 compared to the stiff boots. In conclusion, the soft boots had significantly higher [Formula: see text] EX and running economy, while stiff boots had significantly lower [Formula: see text] EX and intermediate boots significantly lower running economy. Moreover, [Formula: see text] EX appears to be a better indicator of the boot flexural stiffness impact on energy efficiency than running economy.

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Energetically optimal running requires torques about the centre of mass

Journal of The Royal Society Interface ◽

10.1098/rsif.2012.0145 ◽

2012 ◽

Vol 9 (73) ◽

pp. 2011-2015 ◽

Cited By ~ 7

Author(s):

James R. Usherwood ◽

Tatjana Y. Hubel

Keyword(s):

Large Body ◽

The Body ◽

Moment Of Inertia ◽

Mechanical Work ◽

Vertical Force ◽

Centre Of Mass ◽

Pitch Moment ◽

Tail Structure ◽

Reaction Forces ◽

Long Head

Bipedal animals experience ground reaction forces (GRFs) that pass close to the centre of mass (CoM) throughout stance, first decelerating the body, then re-accelerating it during the second half of stance. This results in fluctuations in kinetic energy, requiring mechanical work from the muscles. However, here we show analytically that, in extreme cases (with a very large body pitch moment of inertia), continuous alignment of the GRF through the CoM requires greater mechanical work than a maintained vertical force; we show numerically that GRFs passing between CoM and vertical throughout stance are energetically favourable under realistic conditions; and demonstrate that the magnitude, if not the precise form, of actual CoM-torque profiles in running is broadly consistent with simple mechanical work minimization for humans with appropriate pitch moment of inertia. While the potential energetic savings of CoM-torque support strategies are small (a few per cent) over the range of human running, their importance increases dramatically at high speeds and stance angles. Fast, compliant runners or hoppers would benefit considerably from GRFs more vertical than the zero-CoM-torque strategy, especially with bodies of high pitch moment of inertia—suggesting a novel advantage to kangaroos of their peculiar long-head/long-tail structure.

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Effect of fatigue and gender on kinematics and ground reaction forces variables in recreational runners

PeerJ ◽

10.7717/peerj.4489 ◽

2018 ◽

Vol 6 ◽

pp. e4489 ◽

Cited By ~ 7

Author(s):

Bruno Bazuelo-Ruiz ◽

Juan V. Durá-Gil ◽

Nicolás Palomares ◽

Enrique Medina ◽

Salvador Llana-Belloch

Keyword(s):

Plantar Flexion ◽

Injury Rate ◽

Running Economy ◽

Ground Reaction Forces ◽

Shock Attenuation ◽

Test Protocol ◽

Reaction Forces ◽

Recreational Runners ◽

And Gender ◽

The Impact

The presence of fatigue has been shown to modify running biomechanics. Overall in terms of gender, women are at lower risk than men for sustaining running-related injuries, although it depends on the factors taken into account. One possible reason for these differences in the injury rate and location might be the dissimilar running patterns between men and women. The purpose of this study was to determine the effect of fatigue and gender on the kinematic and ground reaction forces (GRF) parameters in recreational runners. Fifty-seven participants (28 males and 29 females) had kinematic and GRF variables measured while running at speed of 3.3 m s−1 before and after a fatigue test protocol. The fatigue protocol included (1) a running Course-Navette test, (2) running up and down a flight of stairs for 5 min, and (3) performance of alternating jumps on a step (five sets of 1 minute each with 30 resting seconds between the sets). Fatigue decreased dorsiflexion (14.24 ± 4.98° in pre-fatigue and 12.65 ± 6.21° in fatigue condition, p < 0.05) at foot strike phase in females, and plantar flexion (−19.23 ± 4.12° in pre-fatigue and −18.26 ± 5.31° in fatigue condition, p < 0.05) at toe-off phase in males. These changes led to a decreased loading rate (88.14 ± 25.82 BW/s in pre-fatigue and 83.97 ± 18.83 BW/s in fatigue condition, p < 0.05) and the impact peak in females (1.95 ± 0.31 BW in pre-fatigue and 1.90 ± 0.31 BW in fatigue condition, p < 0.05), and higher peak propulsive forces in males (−0.26 ± 0.04 BW in pre-fatigue and −0.27 ± 0.05 BW in fatigue condition, p < 0.05) in the fatigue condition. It seems that better responses to impact under a fatigue condition are observed among women. Further studies should confirm whether these changes represent a strategy to optimize shock attenuation, prevent running injuries and improve running economy.

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The impact of centre of mass kinematics and ground reaction forces on ball release speeds in cricket fast bowling

Sports Technology ◽

10.1080/19346182.2014.893351 ◽

2014 ◽

Vol 7 (1-2) ◽

pp. 4-11 ◽

Cited By ~ 1

Author(s):

Paul S. Glazier ◽

Peter J. Worthington

Keyword(s):

Ground Reaction Forces ◽

Centre Of Mass ◽

Ball Release ◽

Reaction Forces ◽

The Impact

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A Case Study of an Iron-Deficient Female Olympic 1500-m Runner

International Journal of Sports Physiology and Performance ◽

10.1123/ijspp.8.6.695 ◽

2013 ◽

Vol 8 (6) ◽

pp. 695-698 ◽

Cited By ~ 12

Author(s):

Charles R. Pedlar ◽

Gregory P. Whyte ◽

Richard Burden ◽

Brian Moore ◽

Gill Horgan ◽

...

Keyword(s):

Blood Lactate ◽

Lactate Threshold ◽

Venous Blood ◽

Young Female ◽

Running Economy ◽

Iron Deficient ◽

Data Points ◽

And Performance ◽

The Impact

This case study examines the impact of low serum ferritin (sFe) on physiological assessment measures and performance in a young female 1500-m runner undertaking approximately 95–130 km/wk training. The study spans 4 race seasons and an Olympic Games. During this period, 25 venous blood samples were analyzed for sFe and hemoglobin (Hb); running economy, VO2max, and lactate threshold were measured on 6 occasions separated by 8–10 mo. Training was carefully monitored including 65 monitored treadmill training runs (targeting an intensity associated with the onset of blood lactate accumulation) using blood lactate and heart rate. Performances at competitive track events were recorded. All data were compared longitudinally. Mean sFe was 24.5 ± 7.6 μg/L (range 10–47), appearing to be in gradual decline with the exception of 2 data points (37 and 47 μg/L) after parenteral iron injections before championships, when the lowest values tended to occur, coinciding with peak training volumes. Each season, 1500-m performance improved, from 4:12.8 in year 1 to 4:03.5 in year 4. VO2max (69.8 ± 2.0 mL · kg−1 · min−1) and running economy (%VO2max at a fixed speed of 16 km/h; max 87.8%, min 80.3%) were stable across time and lactate threshold improved (from 14 to 15.5 km/h). Evidence of anemia (Hb <12 g/dL) was absent. These unique data demonstrate that in 1 endurance athlete, performance can continue to improve despite an apparent iron deficiency. Raising training volume may have caused increased iron utilization; however, the effect of this on performance is unknown. Iron injections were effective in raising sFe in the short term but did not appear to affect the long-term pattern.

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