Heterogeneous effects of eccentric training and nordic hamstring exercise on the biceps femoris fascicle length based on ultrasound assessment and extrapolation methods: A systematic review of randomised controlled trials with meta-analyses

Abstract

Objective: To systematically review the effects of eccentric training based on biceps femoris fascicle length using ultrasound assessment and extrapolation methods.

Design: Systematic review and meta-analysis of randomised controlled trials.

Data sources: CENTRAL, CINAHL Plus with full text, PubMed and OpenGrey databases were searched on 6 July 2021.

Eligibility criteria for selecting studies: Randomised controlled trials (RCTs) lasting at least four weeks and presenting data about biceps femoris (BF) fascicle length (FL) as an outcome.

Method: Searching databases, screening studies, performing risk of bias assessments and determining the level of evidence (LoE) for each meta-analysis were applied during the study. PRISMA 2020 statement and Cochrane Handbook for Systematic Reviews of Interventions were used as the guidelines of this systematic review.

Results: Eight randomised controlled trials included in meta-analyses. Based on the very low and low LoE, eccentric training has small (g = 0.29, 95% CI [-0.26, 0.85]), moderate (g = 0.72, 95% CI [0.17, 1.28]) and large (g = 2.20, 95% CI [0.99, 3.41]) effect sizes (ES) based on manual linear extrapolation (MLE), panoramic ultrasound scanning and trigonometric equation methods, respectively. Similarly, Nordic hamstring exercise (NHE) has small (g = 0.23 [-1.02, 1.47]), small (g = 0.38, 95% CI [-0.50, 1.27]) and large (g = 1.98, 95% CI [0.52, 3.44]) ES based on the MLE, panoramic ultrasound scanning and trigonometric equation methods, respectively.

Conclusion: ES of eccentric training, including NHE, vary between the MLE, panoramic ultrasound scanning, and equation methods. The relevant scientific community should have a consensus on measurement standards of the BF FL measurements. Further studies can be conducted to compare the effects of eccentric training based on the ultrasound assessment and extrapolation methods.

Fig 1. PRISMA 2020 flow diagram.

This diagram illustrates the eligible study identification, screening, inclusion and exclusion processes of this systematic review.

Fig 2. Risk of bias assessment graph.

This graph shows the general percentage ratio of reviewer authors’ judgements about the risk of bias of each bias item for all included studies (generated via RevMan 5.4.1).

Fig 3. Review authors’ judgements about each risk of bias item for included studies [–58].

Positive (+) values represent a low risk of bias, question marks (?) represent an unclear risk of bias, and negative (-) values represent a high risk of bias (generated via RevMan 5.4.1).

Fig 4. Forest plot effect sizes of eccentric training on biceps femoris fascicle length based on ultrasound assessment and extrapolation methods.

Overall eccentric training has a large effect size on increasing biceps femoris FL (g = 1.06 [0.44, 1.68], I² = 75%). Eccentric training has a small effect based on the manual linear extrapolation method (g = 0.29 [-0.26, 0.85], I² = 31%), a medium effect based on the panoramic ultrasound assessments (g = 0.72 [0.17, 1.28], I² = 0%) and a large effect based on the trigonometric equation method (g = 2.20 [0.99, 3.41], I² = 76%) (created via RevMan 5.4.1).

Fig 5. Funnel plot effect sizes of eccentric training on biceps femoris fascicle length based on the ultrasound assessment and extrapolation methods.

Red coloured squares represent studies that used manual linear extrapolation method, black coloured circles represent studies that used panoramic ultrasound scanning method, and green coloured squares represent studies that used trigonometric equation method. The asymmetry in the figure means a publication bias between the study groups that were used different ultrasound assessment methods. (created via RevMan 5.4.1). Acronyms: SE(SMD), standard error of standardised mean differences; SMD, standardised mean difference.

Fig 6. Forest plot eccentric training-induced mean (cm) changes in biceps femoris fascicle length based on the ultrasound assessment and extrapolation methods.

Eccentric training leads 0.02 cm ([-0.13, 0.17], I² = 55%), 0.47 cm ([0.15, 0.80], I² = 0%), and 1.84 cm ([1.33, 2.34], I² = 52%) increases in biceps femoris FL based on the MLE method, panoramic ultrasound scanning and trigonometric equation methods, respectively (created via RevMan 5.4.1).

Fig 7. Funnel plot eccentric training-induced mean (cm) changes in biceps femoris fascicle length based on the ultrasound assessment and extrapolation methods.

Red coloured squares represent studies that used manual linear extrapolation method, black coloured circles represent studies that used panoramic ultrasound scanning method, and green coloured squares represent studies that used trigonometric equation method. The asymmetry in the figure means a publication bias between the study groups that were used different ultrasound assessment methods (created via RevMan 5.4.1). Acronyms: SE(MD), standard error of mean differences; MD, mean difference.

Fig 8. Forest plot effect sizes Nordic Hamstring Exercise (NHE) on biceps femoris fascicle length based on the ultrasound assessment and extrapolation methods.

The overall effect size of the NHE on increasing biceps femoris FL was large (g = 1.09 [0.16, 2.01], I2 = 79%). NHE has a small effect size on increasing the biceps femoris FL based on the MLE method (g =, 0.23 [-1.02, 1.47], I² = 69%), has a small effect size on increasing biceps femoris FL based on the panoramic ultrasound scanning (g = 0.38 [-0.50, 1.27]), and has a large effect on increasing biceps femoris FL based on the equation methods (g = 1.98 [0.52, 3.44], I² = 79%) (created via RevMan 5.4.1).

Fig 9. Funnel plot effect sizes Nordic hamstring exercise on biceps femoris fascicle length based on the ultrasound assessment and extrapolation methods.

Red coloured squares represent studies that used manual linear extrapolation method, black coloured circles represent studies that used panoramic ultrasound scanning method, and green coloured squares represent studies that used trigonometric equation method. The asymmetry in the figure means a publication bias between the study groups that were used different ultrasound assessment methods (created via RevMan 5.4.1). Acronyms: SE(SMD), standard error of standardised mean differences; SMD, standardised mean difference.

Fig 10. Forest plot Nordic hamstring exercise-induced mean (cm) changes in biceps femoris fascicle length based on the ultrasound assessment and extrapolation methods.

Overall, NHE leads to 1.08 cm increment ([0.09, 2.07], I² = 95%). NHE do leads to 0.24 cm ([-0.52, 1.01], I² = 71%), 0.29 cm ([-0.35, 0.93]) and 2.04 cm ([1.45, 2.63], I² = 34%) increases in the biceps femoris fascicle length based on the MLE, panoramic ultrasound scanning and trigonometric equation methods, respectively (created via RevMan 5.4.1).

Fig 11. Funnel plot Nordic hamstring exercise induced mean (cm) changes in biceps femoris fascicle length based on the ultrasound assessment and extrapolation methods.

Red coloured squares represent studies that used manual linear extrapolation method, black coloured circles represent studies that used panoramic ultrasound scanning method, and green coloured squares represent studies that used trigonometric equation method. The asymmetry in the figure means a publication bias between the study groups that were used different ultrasound assessment methods (created via RevMan 5.4.1). Acronyms: SE(MD), standard error of mean differences; MD, mean difference.

Fig 12. Forest plot effects of 4–6 weeks of Nordic hamstring exercise on the biceps femoris FL based on ultrasound assessment and extrapolation methods.

NHE interventions used trigonometric equation methods for estimating the FL showed large effects sizes (g = 1.89–3.47) on increasing biceps femoris FL, while the six weeks of NHE interventions using the MLE (g = -0.37) or panoramic ultrasound scanning (g = 0.38) methods were not showing even medium effect sizes on increasing biceps femoris FL (created via RevMan 5.4.1).

Fig 13. Funnel plot effects of 4–6 weeks of Nordic hamstring exercise on the biceps femoris FL based on ultrasound assessment and extrapolation methods.

The red coloured square represents a study that used the manual linear extrapolation method, the black coloured circle represent a study that used the panoramic ultrasound scanning method, and the green coloured square and blue coloured triangle represent studies that used the trigonometric equation method. The asymmetry in the figure means a publication bias between the study groups that were used different ultrasound assessment methods (created via RevMan 5.4.1). Acronyms: SE(SMD), standard error of standardised mean differences; SMD, standardised mean difference.