Selecting the number of trials in experimental biomechanics studies

Forrester, Stephanie E.

doi:10.1080/23335432.2015.1049296

Cited by 35 publications

(28 citation statements)

References 22 publications

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“…In this prospective comparative study, eligible participants were pregnant women older than 18 years and beyond 32 weeks of gestation, followed by physiological pregnancy consultation, with a body mass index under 40, and without inflammatory joint diseases or joint hypermobility syndrome, such as Marfan’s syndrome. In biomechanical studies, the number of subjects beyond 10 has an insignificant effect on statistical power [11]. Taking into account the risk of failure of data analysis or during experimentation, we approximated that 13 pregnant women were necessary in this study.…”

Section: Methodsmentioning

confidence: 99%

Is there an impact of feet position on squatting birth position? An innovative biomechanical pilot study

Desseauve

Fradet²,

Lacouture³

et al. 2019

BMC Pregnancy Childbirth

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Background The squatting birth position is widely used for “natural” birth or in countries where childbirth occurs in non-medical facilities. Squatting birth positions, like others, are roughly defined so a biomechanical assessment is required with the availability of noninvasive technology in pregnant women. In practice, we can observe spontaneously two kinds of squatting birth position: on tiptoes and with feet flat. Objective To compare the impact of foot posture on biomechanical parameters considered essential in obstetrical biomechanics during a squatting birth position: on tiptoes versus with feet flat on the floor. Study design Thirteen pregnant women beyond 32 weeks of gestational age who were not in labor were assessed during squatting birth position firstly spontaneously and secondly with the foot posture that was not taken spontaneously (on the tiptoes vs with feet flat). For each position, ANGle of flexion on the spine of the plane of the pelvis external conjugate (ANGec), hip flexion and abduction, and lumbar curve were assessed using an optoelectronic motion capture system and a biomechanical model adapted from the conventional gait model as well as a measuring system of the lumbar curve. Results Spontaneously, 11 out of 13 women squatted on tiptoe at the first test. On tiptoes the hip flexion was lower than with feet flat ( p < 0.02), whereas hip abduction was not significantly different ( p = 0.28). A lower ANGec angle ( p = 0.003) was noticed for the tiptoe position than feet flat. The lumbar curve (lordosis) was more marked for the squatting position on tiptoes than for the position with feet flat ( p < 0.001). On tiptoes no woman had a pelvic inlet plane perpendicular to the spine and none had a flat back or kyphosis. No woman on tiptoes fulfilled the two conditions necessary for the position that we consider optimal. Conclusion In squatting birth position, foot posture has a biomechanical impact on lumbar curve and pelvic orientation. When comparing squatting positions (on tiptoes vs feet flat), feet flat on the ground is closer to optimal birth conditions than on tiptoes.

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Section: Methodsmentioning

confidence: 99%

Is there an impact of feet position on squatting birth position? An innovative biomechanical pilot study

Desseauve

Fradet²,

Lacouture³

et al. 2019

BMC Pregnancy Childbirth

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“…Based on prior sample size 25 calculations, 40 athletes (20 females and 20 males) from different fields of sport participated in this study.…”

Section: Methodsmentioning

confidence: 99%

“…According to the relevant literature, this number of participants performing in multiple trials was sufficient and viable for application to this type of study, to ensure good statistical viability with regards to the parameters in question. 25 26 …”

Section: Methodsmentioning

confidence: 99%

The effects of a single session of lumbar spinal manipulative therapy in terms of physical performance test symmetry in asymptomatic athletes: a single-blinded, randomised controlled study.

Alvarenga

Fujikawa

João

et al. 2018

BMJ Open Sport Exerc Med

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Background and aimMusculoskeletal disorders in athletes, including spinal biomechanical dysfunctions, are believed to negatively influence symmetry. Spinal manipulative therapy (SMT) is recognised as a safe and effective treatment for musculoskeletal disorders, but there is little evidence about whether it can be beneficial in symmetry. Therefore, this study aimed to measure the effects of lumbar SMT in symmetry.MethodsForty asymptomatic athletes participated in the study. The randomisation procedure was performed according to the following group allocation: group 1 (SMT) and group 2 (SHAM). Each participant completed a physical activity questionnaire, and also underwent clinical and physical evaluation for inclusion according to eligibility criteria. Statistical significance (P<0.05) between groups and types of therapy were calculated by physical performance tests symmetry (static position, squat and counter movement jump (CMJ), pre- and post-SMT and SHAM. There were 14 trials of three symmetry tests for each participant, for a total of 560 trials.ResultsLumbar SMT produced immediate effects in symmetry in the static position; however, the same effects were not found in squat and CMJ on symmetry 1. Therefore, our results showed a significant difference in pre- (mean 16.3%) and post-lumbar SMT (mean 3.7%) in static symmetry. However, symmetry 2 showed no statistical significant differences for any of the tests and intervention groups. No statistically significant effects in symmetry pre- to post-SHAM were found in any of the tests.ConclusionsStatistically significant differences were found in lumbar SMT, but only for static symmetry. These findings suggest that SMT was effective in producing immediate effects in symmetry in the static position, but none in dynamic tests. Future studies could address our study's limitations.Clinical trials register numberNCT03361592.

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“…In a technique exploring the bivariate plots of intra-participant data (Mullineaux 2017), it is recommended that a minimum of 10 trials are used as this leads to a sufficiently low bias between the actual area and ellipse quantified area (Jackson et al 2011). Given the complexity of assessing how many trials are required in biomechanical research, and independently of the number of subjects as applicable to this situation on intra-participant data, for typical simulation criteria a total of 9 ± 8 trials are required (mean ± 95% confidence intervals; Forrester 2015). Consequently, it is proposed there is no set minimum, although approximately nine trials might be advisable to use for this outlier detection method.…”

Section: Discussionmentioning

confidence: 99%

Error and anomaly detection for intra-participant time-series data

Mullineaux

Irwin

2017

International Biomechanics

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Identification of errors or anomalous values, collectively considered outliers, assists in exploring data or through removing outliers improves statistical analysis. In biomechanics, outlier detection methods have explored the 'shape' of the entire cycles, although exploring fewer points using a 'moving-window' may be advantageous. Hence, the aim was to develop a moving-window method for detecting trials with outliers in intra-participant time-series data. Outliers were detected through two stages for the strides (mean 38 cycles) from treadmill running. Cycles were removed in stage 1 for one-dimensional (spatial) outliers at each time point using the median absolute deviation, and in stage 2 for two-dimensional (spatial-temporal) outliers using a moving window standard deviation. Significance levels of the t-statistic were used for scaling. Fewer cycles were removed with smaller scaling and smaller window size, requiring more stringent scaling at stage 1 (mean 3.5 cycles removed for 0.0001 scaling) than at stage 2 (mean 2.6 cycles removed for 0.01 scaling with a window size of 1). Settings in the supplied Matlab code should be customised to each data set, and outliers assessed to justify whether to retain or remove those cycles. The method is effective in identifying trials with outliers in intra-participant time series data.

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Selecting the number of trials in experimental biomechanics studies

Cited by 35 publications

References 22 publications

Is there an impact of feet position on squatting birth position? An innovative biomechanical pilot study

Is there an impact of feet position on squatting birth position? An innovative biomechanical pilot study

The effects of a single session of lumbar spinal manipulative therapy in terms of physical performance test symmetry in asymptomatic athletes: a single-blinded, randomised controlled study.

Error and anomaly detection for intra-participant time-series data

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