Browsing by Person "Li, Siu Nam"

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Constant low-to-moderate mechanical asymmetries during a treadmill graded exercise test
(Routledge, 2021-06-27) Girard, Olivier; Van Alsenoy, Ken K.; Li, Siu Nam; Ryu, Joong Hyun; Peeling, Peter
This study describes asymmetry in key mechanical variables during a treadmill-based, running graded exercise test (GXT). Twenty-one recreationally trained male runners completed a continuous, maximal GXT on an instrumented treadmill, starting at 9 km.h−1 with speed increases of +0.5 km.h−1 every 30 s, for the determination of ventilatory threshold (VT), respiratory compensation point (RCP), and maximal oxygen uptake (MAX). Ground reaction forces were recorded continuously and subsequently averaged from 10 consecutive steps corresponding to VT, RCP and MAX intensity stages (13.4 ± 1.2 km.h−1, 16.0 ± 1.6 km.h−1 and 18.2 ± 1.5 km.h−1, respectively). Asymmetry scores were assessed from the “symmetry angle” (SA) formulae, where a score of 0%/100% indicates perfect symmetry/asymmetry; these were then compared between the three intensity stages. There was no influence of exercise intensity on SA scores for any of the sixteen biomechanical variables (P > 0.222). The group mean SA scores did not exceed 1.5% for spatio-temporal variables (contact time, aerial time, frequency and step length). There were larger mean SA scores for mean loading rate (3.7 ± 2.7%) and most spring-mass model variables (vertical stiffness: 2.2 ± 1.6% and leg stiffness: 1.7 ± 1.4%). The SA scores were ∼1.0–3.5% for braking and propulsive phase durations, peak forces, and resulting impulses. Lower extremities behave similarly at submaximal and maximal intensities during GXT, indicating that runners maintained relatively even strides as intensity increased. However, practitioners must be careful not to infer the presence of asymmetry during GXT based on a single variable, given the lower SA scores for spatio-temporal parameters.
Detecting mechanical breakpoints during treadmill-based graded exercise test: Relationships to ventilatory thresholds
(Routledge, 2021-09-15) Li, Siu Nam; Peeling, Peter; Hansen, Clint; Van Alsenoy, Ken K.; Ryu, Joong Hyun; Girard, Olivier
While changes in cardiorespiratory variables during graded exercise tests (GXTs) are well described, less is known about running mechanical alterations. We determined mechanical breakpoints during GXT and compared their temporal location with thresholds in ventilation. Thirty-one recreational male runners completed continuous GXT on an instrumented treadmill, starting at 2.5 m.s with velocity increases of + 0.14 m.s every 30 s. Subsequently, the first and second ventilatory thresholds (VT1 and VT2) were determined from expired gases. Spatio-temporal and antero-posterior force variables, and spring-mass model characteristics were averaged for each stage. Mechanical breakpoints were detected using a linear fit process that partitioned the timeseries into two regions and minimised the error sum of squares. All measurements were normalised to % GXT duration for subsequent comparisons. Fifteen out of 16 mechanical variables (all except leg stiffness) displayed breakpoints occurring between 61.9% and 82.3% of GXT duration; these occurred significantly later than VT1 (46.9 ± 6.4% of GXT duration, < 0.05). Mechanical breakpoints for eight variables (step frequency, aerial time, step length, peak push-off force, braking impulse, peak vertical force, maximal downward vertical displacement and leg compression) occurred at a time point not different to VT2 (75.3 ± 6.2% of GXT duration; all > 0.05). Relationships between mechanical breakpoints and either VT1 or VT2 were weak (all < 0.25). During treadmill GXT, breakpoints can be detected for the vast majority of mechanical variables (except leg stiffness), yet these are not related with ventilatory thresholds.