Aim: Prediction intervals are a useful measure of uncertainty for meta‐analyses that capture the likely effect size of a new (similar) study based on the included studies. In comparison, confidence intervals reflect the uncertainty around the point estimate but provide an incomplete summary of the underlying heterogeneity in the meta‐analysis. This study aimed to estimate (i) the proportion of meta‐analysis studies that report a prediction interval in sports medicine; and (ii) the proportion of studies with a discrepancy between the reported confidence interval and a calculated prediction interval.Methods: We screened, at random, 1500 meta‐analysis studies published between 2012 and 2022 in highly ranked sports medicine and medical journals. Articles that used a random effect meta‐analysis model were included in the study. We randomly selected one meta‐analysis from each article to extract data from, which included the number of estimates, the pooled effect, and the confidence and prediction interval.Results: Of the 1500 articles screened, 866 (514 from sports medicine) used a random effect model. The probability of a prediction interval being reported in sports medicine was 1.7% (95% CI = 0.9%, 3.3%). In medicine the probability was 3.9% (95% CI = 2.4%, 6.6%). A prediction interval was able to be calculated for 220 sports medicine studies. For 60% of these studies, there was a discrepancy in study findings between the reported confidence interval and the calculated prediction interval. Prediction intervals were 3.4 times wider than confidence intervals.Conclusion: Very few meta‐analyses report prediction intervals and hence are prone to missing the impact of between‐study heterogeneity on the overall conclusions. The widespread misinterpretation of random effect meta‐analyses could mean that potentially harmful treatments, or those lacking a sufficient evidence base, are being used in practice. Authors, reviewers, and editors should be aware of the importance of prediction intervals.

Introduction: There is a lack of definitive evidence supporting deficits in voluntary activation in participants with prior hamstring injury; moreover, it remains unknown if spinal mechanisms contribute to suspected deficits. Purpose: This study aimed to determine the effect of prior hamstring strain injury on knee flexor concentric and eccentric strength, voluntary activation, surface electromyographic (sEMG) activity, and stretch and tendon reflex amplitudes. Methods: Twenty-five participants were recruited, 12 with a history of unilateral hamstring strain injury of at least moderate severity. Voluntary activation, strength, and sEMG activity were recorded during maximal eccentric and concentric knee flexor contractions at 60°·s⁻¹. Stretch and tendon reflexes were also recorded at rest. Results: Previously injured limbs exhibited lower levels of voluntary activation (mean difference = −24.1%, 95% confidence interval [CI] = −34.1% to −14.0%, P < 0.001), strength (mean difference vs control group = −0.37 Nm·kg⁻¹, 95% CI = −0.71% to −0.03 N·m·kg⁻¹, P = 0.03), and normalized sEMG (mean difference = −17%, 95% CI = −32% to −2%, P = 0.02) during maximal eccentric knee flexor contractions compared with control group. No such differences were seen in concentric contractions. Stretch reflexes (mean difference = −3.8%, 95% CI = −6.8 to −0.8, P = 0.02) and tendon reflexes (mean difference = −13%, 95% CI = −26% to 0%, P = 0.04) were also lower in previously injured compared with control biceps femoris muscles. Conclusion: Moderate to severe hamstring strain injury is associated with long-term deficits in voluntary activation during maximal eccentric contraction. Hamstring injury history is also associated with deficits in stretch reflex and tendon reflex amplitude.

Purpose: The use of electrical stimulation to assess voluntary activation of muscle/s is a popular method employed in numerous exercise science and health research settings. This Delphi study aimed to collate expert opinion and provide recommendations for best practice when using electrical stimulation during maximal voluntary contractions. Methods: A two-round Delphi study was undertaken with 30 experts who completed a 62-item questionnaire (Round 1) comprising of open- and closed-ended questions. Consensus was assumed if ≥ 70% of experts selected the same response; such questions were removed from the subsequent Round 2 questionnaire. Responses were also removed if they failed to meet a 15% threshold. Open-ended questions were analysed and converted into closed-ended questions for Round 2. It was assumed there was no clear consensus if a question failed to achieve a ≥ 70% response in Round 2. Results: A total of 16 out of 62 (25.8%) items reached consensus. Experts agreed that electrical stimulation provides a valid assessment of voluntary activation in specific circumstances, such as during maximal contraction, and this stimulation can be applied at either the muscle or the nerve. Experts recommended using doublet stimuli, self-adhesive electrodes, a familiarisation session, real-time visual or verbal feedback during the contraction, a minimum current increase of + 20% to ensure supramaximal stimulation, and manually triggering stimuli. Conclusion: The results of this Delphi consensus study can help researchers make informed decisions when considering technical parameters when designing studies involving electrical stimulation for the assessment of voluntary activation.

Strength assessment and comparison to normative values are an important benchmarking tool in human health and performance. However, population specific normative data are several decades old, lack information about adolescent and adult strength levels and are not representative of the strength levels of strength trained individuals. The purpose of this study was to develop contemporary strength norms for the squat, bench press, and deadlift using powerlifters competing in un-equipped, drug-tested competitions. Retrospective cross-sectional analysis. Retrospective data from global drug-tested, unequipped powerlifting competitions were collated with 809,986 samples (571,650 males, 238,336 females) included. Strength was assessed according to sex, United Nations age classifications, and competitive powerlifting weight class. Strength was expressed relatively (ratio of weight lifted/bodyweight) and computed for the 10th-90th percentile for each of the above categories. Relative strength was greatest for young adults (18-35 years; 90th percentile for squat [male: 2.83 × bodyweight, female: 2.26], bench press [male: 1.95, female: 1.35], deadlift [male: 3.25, female: 2.66]) before declining thereafter for all three exercises. Although lower than their younger counterparts, very old adults (>80 years) had 90th percentile data for the squat of male: 1.72 and female: 1.01, bench press: male: 1.31 and female: 0.92, and deadlift: male: 2.30 and female: 1.68. These findings provide a comprehensive, accurate and precise representation of strength for drug-tested, unequipped powerlifters in each category and serve as a point of reference for other trained population groups. To facilitate uptake and ease of comparison, we have developed a freely available online tool (www.thestrengthinitiative.com).

The aim of the INveStigating ProblEmatic Clinical Trials in Systematic Reviews (INSPECT-SR) project is to develop a tool to identify problematic RCTs in systematic reviews. In stage 1 of the project, a list of potential trustworthiness checks was created. The checks on this list must be evaluated to determine which should be included in the INSPECT-SR tool. We attempted to apply 72 trustworthiness checks to randomized controlled trials (RCTs) in 50 Cochrane reviews. For each, we recorded whether the check was passed, failed, or possibly failed or whether it was not feasible to complete the check. Following application of the checks, we recorded whether we had concerns about the authenticity of each RCT. We repeated each meta-analysis after removing RCTs flagged by each check and again after removing RCTs where we had concerns about authenticity to estimate the impact of trustworthiness assessment. Trustworthiness assessments were compared to Risk of Bias and Grading of Recommendations Assessment, Development and Evaluation (GRADE) assessments in the reviews. Ninety-five RCTs were assessed. Following application of the checks, assessors had some or serious concerns about the authenticity of 25% and 6% of the RCTs, respectively. Removing RCTs with either some or serious concerns resulted in 22% of meta-analyses having no remaining RCTs. However, many checks proved difficult to understand or implement, which may have led to unwarranted skepticism in some instances. Furthermore, we restricted assessment to meta-analyses with no more than five RCTs (54% contained only 1 RCT), which will distort the impact on results. No relationship was identified between trustworthiness assessment and Risk of Bias or GRADE. This study supports the case for routine trustworthiness assessment in systematic reviews, as problematic studies do not appear to be flagged by Risk of Bias assessment. The study produced evidence on the feasibility and impact of trustworthiness checks. These results will be used, in conjunction with those from a subsequent Delphi process, to determine which checks should be included in the INSPECT-SR tool. Systematic reviews collate evidence from randomized controlled trials (RCTs) to find out whether health interventions are safe and effective. However, it is now recognized that the findings of some RCTs are not genuine, and some of these studies appear to have been fabricated. Various checks for these "problematic" RCTs have been proposed, but it is necessary to evaluate these checks to find out which are useful and which are feasible. We applied a comprehensive list of "trustworthiness checks" to 95 RCTs in 50 systematic reviews to learn more about them and to see how often performing the checks would lead us to classify RCTs as being potentially inauthentic. We found that applying the checks led to concerns about the authenticity of around 1 in three RCTs. However, we found that many of the checks were difficult to perform and could have been misinterpreted. This might have led us to be overly skeptical in some cases. The findings from this study will be used, alongside other evidence, to decide which of these checks should be performed routinely to try to identify problematic RCTs, to stop them from being mistaken for genuine studies and potentially being used to inform health care decisions.