Sample size justifications in Gait & Posture

BACKGROUND: Context regarding how researchers determine the sample size of their experiments is important for interpreting the results and determining their value and meaning. Between 2018 and 2019, the journal Gait & Posture introduced a requirement for sample size justification in their author guidelines. RESEARCH QUESTION: How frequently and in what ways are sample sizes justified in Gait & Posture research articles and was the inclusion of a guideline requiring sample size justification associated with a change in practice? METHODS: The guideline was not in place prior to May 2018 and was in place from 25th July 2019. All articles in the three most recent volumes of the journal (84-86) and the three most recent, pre-guideline volumes (60-62) at time of preregistration were included in this analysis. This provided an initial sample of 324 articles (176 pre-guideline and 148 post-guideline). Articles were screened by two authors to extract author data, article metadata and sample size justification data. Specifically, screeners identified if (yes or no) and how sample sizes were justified. Six potential justification types (Measure Entire Population, Resource Constraints, Accuracy, A priori Power Analysis, Heuristics, No Justification) and an additional option of Other/Unsure/Unclear were used. RESULTS: In most cases, authors of Gait & Posture articles did not provide a justification for their study's sample size. The inclusion of the guideline was associated with a modest increase in the percentage of articles providing a justification (16.6-28.1%). A priori power calculations were the dominant type of justification, but many were not reported in enough detail to allow replication. SIGNIFICANCE: Gait & Posture researchers should be more transparent in how they determine their sample sizes and carefully consider if they are suitable. Editors and journals may consider adding a similar guideline as a low-resource way to improve sample size justification reporting

Sprint performance and force-velocity profiling does not differ between artificial turf and concrete

Purpose: Force-velocity-power (F-v-P) profiling can illustrate an individual’s sprinting capabilities, but no study has explored the effect of different running surfaces on F-v-P outcomes. Method: Twelve elite youth football players (age 16.3 0.5 years, mass 67.3 5.4 kg, height 176.2 4.6 cm) performed two 30 m sprints on concrete and artificial turf in a randomised order on two testing days. Differences between surfaces were determined using repeated-measures ANOVA (P < 0.05), whilst the coefficient of variation (CV), smallest worthwhile change and standard error of measurement were calculated to quantify reliability. Results: No significant differences were found between surfaces over the average of two days. High reliability was evident for 30 m sprint time, theoretical maximum horizontal velocity and ratio of force on both surfaces (CV 5%), while the remaining outputs were not reliable (CV >10%). Conclusion: These findings show that F-v-P profiling does not differ between concrete and artificial turf. However, higher variability on the more unfamiliar concrete surface suggests that the testing surface should match the playing surface. Since the standard error of measurement is larger than the smallest worthwhile change, the ability of this method to monitor seasonal changes may be limited in youth elite soccer players

The effects of the Nordic hamstring exercise on sprint performance and eccentric knee flexor strength: A systematic review and meta-analysis of intervention studies among team sport players

The primary aim of this study was to investigate the effects of the Nordic hamstring exercise (NH E ) on sprint performance (i.e., 5, 10 and 20 m) and explore associations between study characteristics and sprint outcomes in team sport players. Secondary aims were to (1) investigate the effects of the NH E on eccentric strength of the knee flexors (ES KF ) with categorical subgroup analysis to determine differences between recreationally, well-trained individuals and young athletes, (2) determine the relation between ES KF and sprint performance in team sport players, and (3) explore the effect of study characteristics (i.e., weekly volume, time duration and body mass) on ES KF .Medicin

A Systematic Review and Meta-Analysis of Crossover Studies Comparing Physiological, Perceptual and Performance Measures Between Treadmill and Overground Running

Background Treadmills are routinely used to assess running performance and training parameters related to physiological or perceived effort. These measurements are presumed to replicate overground running but there has been no systematic review comparing performance, physiology and perceived effort between treadmill and overground running. Objective The objective of this systematic review was to compare physiological, perceptual and performance measures between treadmill and overground running in healthy adults.MethodsAMED (Allied and Contemporary Medicine), CINAHL (Cumulative Index to Nursing and Allied Health), EMBASE, MEDLINE, SCOPUS, SPORTDiscus and Web of Science databases were searched from inception until May 2018. Included studies used a crossover study design to compare physiological (oxygen uptake [VO-2], heart rate [HR], blood lactate concentration [La]), perceptual (rating of perceived exertion [RPE] and preferred speed) or running endurance and sprint performance (i.e. time trial duration or sprint speed) outcomes between treadmill (motorised or non-motorised) and overground running. Physiological outcomes were considered across submaximal, near-maximal and maximal running intensity subgroups. Meta-analyses were used to determine mean difference (MD) or standardised MD (SMD) 95% confidence intervals. Results Thirty-four studies were included. Twelve studies used a 1% grade for the treadmill condition and three used grades >1%. Similar (V) over dotO(2) but lower La occurred during submaximal motorised treadmill running at 0% ((V) over dot O-2 MD: -0.55 0.93mL/kg/min; La MD: -1.26 +/- 0.71mmol/L) and 1% ((V) over dotO(2) MD: 0.37 +/- 1.12mL/kg/min; La MD: -0.52 +/- 0.50mmol/L) grade than during overground running. HR and RPE during motorised treadmill running were higher at faster submaximal speeds and lower at slower submaximal speeds than during overground running. (V) over dotO(2) (MD: -1.25 +/- 2.09mL/kg/min) and La (MD: -0.54 +/- 0.63mmol/L) tended to be lower, but HR (MD: 0 +/- 1bpm), and RPE (MD: -0.4 +/- 2.0units [6-20 scale]) were similar during near-maximal motorised treadmill running to during overground running. Maximal motorised treadmill running caused similar (V) over dotO(2) (MD: 0.78 +/- 1.55mL/kg/min) and HR (MD: -1 +/- 2bpm) to overground running. Endurance performance was poorer (SMD: -0.50 +/- 0.36) on a motorised treadmill than overground but sprint performance varied considerably and was not significantly different (MD: -1.4 +/- 5.8km/h). Conclusions Some, but not all, variables differ between treadmill and overground running, and may be dependent on the running speed at which they are assessed. Protocol registration (PROSPERO International Prospective Register of Systematic Reviews)

Effects of ankle position during the Nordic Hamstring exercise on range of motion, heel contact force and hamstring muscle activation

One of the main benefits of the Nordic Hamstring Exercise (NHE) is that it can be performed without the need of any extra material. However, numerous technical execution variables such as the ankle and pelvis position can influence the performance. The primary aims of this study were to investigate the effects of ankle position (i.e., plantar or dorsal flexion) on Nordic Hamstring Break Point (NHBP), repetition time and heel contact force. A secondary aim was to investigate differences in biceps femoris long head and semitendinosus muscle activation. Male professional field hockey players (n = 12) volunteered for the study. Paired t-tests were used to analyse the effect of ankle position on muscle NHBP, eccentric peak torque and repetition time. Ankle dorsal flexion resulted in a higher NHBP (p = 0.002, effect size [ES] = 1.48 [0.57 to 2.38]), repetition time (p = 0.004, ES = 0.98 [0.24 to 1.72]) and both absolute and relative heel contact force (p = 0.028, ES = 0.67 [0.01 to 1.34], p = 0.017, ES = 0.76 [0.07 to 1.44], respectively) compared to plantar flexion. Muscle activation was not significant different. This study showed a higher NHBP, absolute and relative heel contact force and repetition time with a dorsal flexed ankle vs. a plantar flexed ankle in the NHE, without changes in hamstrings muscle activation.Medicin