Background

Exposure to increased mechanical loading during physical training can lead to increased tendon stiffness. However, the loading regimen that maximises tendon adaptation and the extent to which adaptation is driven by changes in tendon material properties or tendon geometry is not fully understood.

Objective

To determine (1) the effect of mechanical loading on tendon stiffness, modulus and cross-sectional area (CSA); (2) whether adaptations in stiffness are driven primarily by changes in CSA or modulus; (3) the effect of training type and associated loading parameters (relative intensity; localised strain, load duration, load volume and contraction mode) on stiffness, modulus or CSA; and (4) whether the magnitude of adaptation in tendon properties differs between age groups.

Methods

Five databases (PubMed, Scopus, CINAHL, SPORTDiscus, EMBASE) were searched for studies detailing load-induced adaptations in tendon morphological, material or mechanical properties. Standardised mean differences (SMDs) with 95% confidence intervals (CIs) were calculated and data were pooled using a random effects model to estimate variance. Meta regression was used to examine the moderating effects of changes in tendon CSA and modulus on tendon stiffness.

Results

Sixty-one articles met the inclusion criteria. The total number of participants in the included studies was 763. The Achilles tendon (33 studies) and the patella tendon (24 studies) were the most commonly studied regions. Resistance training was the main type of intervention (49 studies). Mechanical loading produced moderate increases in stiffness (standardised mean difference (SMD) 0.74; 95% confidence interval (CI) 0.62–0.86), large increases in modulus (SMD 0.82; 95% CI 0.58–1.07), and small increases in CSA (SMD 0.22; 95% CI 0.12–0.33). Meta-regression revealed that the main moderator of increased stiffness was modulus. Resistance training interventions induced greater increases in modulus than other training types (SMD 0.90; 95% CI 0.65–1.15) and higher strain resistance training protocols induced greater increases in modulus (SMD 0.82; 95% CI 0.44–1.20; p = 0.009) and stiffness (SMD 1.04; 95% CI 0.65–1.43; p = 0.007) than low-strain protocols. The magnitude of stiffness and modulus differences were greater in adult participants.

Conclusions

Mechanical loading leads to positive adaptation in lower limb tendon stiffness, modulus and CSA. Studies to date indicate that the main mechanism of increased tendon stiffness due to physical training is increased tendon modulus, and that resistance training performed at high compared to low localised tendon strains is associated with the greatest positive tendon adaptation.

PROSPERO registration no.: CRD42019141299.

中文翻译：

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健康下肢肌腱对机械负荷的机械、材料和形态适应：系统回顾和荟萃分析

背景

在体能训练期间承受增加的机械负荷会导致肌腱僵硬增加。然而，最大限度地提高肌腱适应性的加载方案以及肌腱材料特性或肌腱几何形状的变化驱动适应性的程度尚不完全清楚。

客观的

确定 (1) 机械载荷对肌腱刚度、模量和横截面积 (CSA) 的影响；(2) 刚度的适应是否主要由 CSA 或模量的变化驱动；(3) 训练类型和相关负荷参数（相对强度、局部应变、负荷持续时间、负荷量和收缩模式）对刚度、模量或 CSA 的影响；(4)不同年龄组肌腱特性的适应程度是否不同。

方法

检索了五个数据库（PubMed、Scopus、CINAHL、SPORTDiscus、EMBASE），以查找详细介绍负荷引起的肌腱形态、材料或机械性能适应性的研究。计算具有 95% 置信区间 (CI) 的标准化平均差 (SMD)，并使用随机效应模型汇集数据以估计方差。Meta 回归用于检查肌腱 CSA 和模量变化对肌腱刚度的调节作用。

结果

六十一篇文章符合纳入标准。纳入研究的参与者总数为 763 人。跟腱（33 项研究）和髌腱（24 项研究）是最常研究的区域。阻力训练是主要的干预类型（49 项研究）。机械载荷导致刚度适度增加（标准化平均差 (SMD) 0.74；95% 置信区间 (CI) 0.62–0.86），模量大幅增加（SMD 0.82；95% CI 0.58–1.07），CSA 小幅增加（ SMD 0.22；95% CI 0.12–0.33）。元回归表明，刚度增加的主要调节因素是模量。与其他训练类型相比，阻力训练干预引起的模量增加更大（SMD 0.90；95% CI 0.65–1.15），较高的应变阻力训练方案引起模量更大的增加（SMD 0.82；95% CI 0.44–1.20；p = 0.009 ）  ，刚度（SMD 1.04；95% CI 0.65–1.43；p  = 0.007）高于低应变方案。成年参与者的刚度和模量差异更大。

结论

机械负荷导致下肢肌腱刚度、模量和 CSA 的积极适应。迄今为止的研究表明，由于体能训练而增加肌腱硬度的主要机制是增加肌腱模量，与低局部肌腱应变相比，在高强度下进行的阻力训练与最大的正向肌腱适应相关。

PROSPERO 注册号：CRD42019141299。