The Influence of General and Local Muscle Fatigue on Kinematics and Plantar Pressure Distribution during Running: A Systematic Review and Meta-Analysis

atigue has the potential to alter how impact forces are absorbed during running, heighten- ing the risk of injury. Con icting ndings exist regarding alterations in both kinematics and plantar pressure. Thus, this systematic review and subsequent meta-analysis were conducted to investigate the impact of general and localized muscle fatigue on kinematics and plantar pressure distribution during running. Initial searches were executed on 30 November 2021 and updated on 29 April 2023, encompassing PubMed, The Cochrane Library, SPORTDiscus, and Web of Science without imposing any restrictions on publication dates or employing additional lters. Our PECOS criteria included cross-sectional studies on healthy adults during their treadmill running to mainly evaluate local muscle fatigue, plantar pressure distribution, biomechanics of running (kinematics, kinetics, and EMG results), and temporospatial parameters. The literature search identi ed 6626 records, with 4626 studies removed for titles and abstract screening. Two hundred and one articles were selected for full-text screening, and 20 studies were included in qualitative data synthesis. The pooled analysis showed a non-signi cant decrease

local muscle fatigue, plantar pressure distribution, biomechanics of running (kinematics, kinetics, and EMG results), and temporospatial parameters. The literature search identi ed 6626 records, with 4626 studies removed for titles and abstract screening. Two hundred and one articles were selected for full-text screening, and 20 studies were included in qualitative data synthesis. The pooled analysis showed a non-signi cant decrease in maximum pressure under the right forefoot's metatarsus, which was more than the left rearfoot after local muscle fatigue at a velocity of 15 km/h (p-values = 0.48 and 0.62). The results were homogeneous and showed that local muscle fatigue did not signi cantly affect the right forefoot's stride frequency and length (p-values = 0.75 and 0.38). Strength training for the foot muscles, mainly focusing on the dorsi exors, is recommended to prevent running-related injuries. Utilizing a standardized knee and ankle joint muscle fatigue assessment protocol is advised. Future experiments should focus on various shoes for running and varying foot strike patterns for injury prevention. Keywords:running; local muscle fatigue; treadmill; plantar pressure distribution 1. Introduction During running, the foot is subjected to forces equivalent to two to three times the runner's body weight. The lower extremity muscles are crucial in providing effective shock absorption to prevent incorrect or excessive loading of the passive musculoskeletal system, primarily through eccentric contraction of the plantar exors [1]. When these muscles experience fatigue, their ability to adequately absorb impact forces diminishes, potentially affecting the passive musculoskeletal system and elevating the risk of running- related injuries. Over 90% of running-related issues are related to the lower extremities, with approximately one-third involving the knee, lower leg, and foot [2,3]. The annual incidence of lower extremity problems among runners ranges from 19.4% to 79.3% [4]. Numerous studies have demonstrated the correlation between muscular fatigue and the Sports2023,11, 241.

Sports2023,11, 241 2 of 27 risk of injury [5,6]. However, despite this body of research, how fatigue speci cally alters foot loading remains unclear. Understanding these changes in foot loading due to fatigue is vital for tailoring injury-preventative training recommendations, particularly for runners with a history of lower extremity injuries, who face an increased risk of re-injury [5,6]. In an ideal scenario, preventing running injuries before they manifest is crucial [3]. However, the surge in runners has been accompanied by a rise in associated health issues, predominantly affecting the lower limbs [7]. Multiple studies have highlighted the connection between fatigue and injury [3,8], yet the exact relationship between injuries and foot strike patterns remains elusive [9]. The exploration of the effects of general and muscle fatigue on plantar pressure distribution and increased ground reaction force during running has seen a signi cant increase in research since 2006. However, due to a wide array of results, the precise impact of fatigue remains unclear. In a meta-analysis examining the alteration of ground reaction force following fatigue, Zadpoor and Nikooyan [10] highlighted that most studies have primarily focused on the active peak vertical ground reaction force, given its re ection of muscular reaction during ground contact. Two major theories dominate the ongoing debate on this subject. The rst theory posits that fatigue diminishes the capacity for adequate shock absorption, causing an increase in ground reaction force to counterbalance this effect. On the other hand, the second theory suggests a reduction in ground reaction force due to the human body's protective strategy to prevent injuries [10]. The meta-analysis incorporated eight studies that assessed the active peak of the ground reaction force using force plates before and after fatigue induced by running. Among these, three studies demonstrated a signi cant decrease [11–13], while four articles indicated minor, non- signi cant changes [14–16]. Another study explored ground reaction force during running after inducing local muscle fatigue in the dorsi exors and invertors of the foot [17]. The ndings revealed a non-signi cant increase in dorsi exors and a reduction in ground reaction force due to inversion.

studies demonstrated a signi cant decrease [11–13], while four articles indicated minor, non- signi cant changes [14–16]. Another study explored ground reaction force during running after inducing local muscle fatigue in the dorsi exors and invertors of the foot [17]. The ndings revealed a non-signi cant increase in dorsi exors and a reduction in ground reaction force due to inversion. Other studies examining ground reaction forces have revealed con icting results. Morin et al. [18] and Morin et al. [19] observed a signi cant reduction in ground reaction force after extreme fatigue induced by either a 24-h treadmill run or an ultra-mountain marathon. The decrease ranged from 2.24 to 2.14 times the body mass in one study and 2.32 to 2.17 times in another [18,19]. Quammen et al. [20] compared two different fatigue protocols. One protocol involved strength tests and sprints, while the other incorporated strength tests followed by a 30-min treadmill run. Surprisingly, both protocols led to a non-signi cant increase in the active peak of the ground reaction force. Studies demonstrate varied plantar pressure distribution across different foot areas following running, ranging from 10 km to a full marathon and even 30-min runs [21,22]. Forefoot pressure speci cally increases after running distances of 10 km to a marathon and during 30-min runs [21–23]; this heightened forefoot pressure is also noted after inducing local fatigue in the plantar exors and dorsi exors [24]. However, the effect of running- induced fatigue on pressure distribution across different foot areas remains unclear. Some studies have reported decreased pressure under the heel [2,21,22,25], while others have observed a signi cant increase [22,26]. Pressure under the toes was signi cantly reduced in some instances [2,24], while two other studies found no signi cant differences [21,26]. The lack of consensus can be attributed to variations in fatigue protocols and the speci c foot areas examined. Another challenge lies in understanding how fatigue in uences foot strike patterns during running. Although it is commonly assumed that fatigue alters foot strike patterns, conclusive evidence is lacking [27,28]. Fatigue may lead to runners modifying their foot strikes during

[21,26]. The lack of consensus can be attributed to variations in fatigue protocols and the speci c foot areas examined. Another challenge lies in understanding how fatigue in uences foot strike patterns during running. Although it is commonly assumed that fatigue alters foot strike patterns, conclusive evidence is lacking [27,28]. Fatigue may lead to runners modifying their foot strikes during running, potentially increasing the risk of injury [5,6]. Therefore, determining whether fatigue induces muscular imbalances and alters foot strike patterns is crucial for injury prevention [29]. Fatigue exerts an impact on both stride frequency and stride length during running. Some studies have shown a decrease in stride frequency and an increase in stride length[2,15].

Sports2023,11, 241 3 of 27 However, there were also instances of only minor changes [30] or even no changes in stride frequency [25]. Additionally, treadmill running introduces alterations in stride frequency [2,31–33]. At moderate speeds on a treadmill, there is a tendency for a reduction in stride length and an increase in stride frequency compared to natural ground running [34]. However, it is essential to note that the in uence of the treadmill on running movements has led to controversial discussions regarding the results [2]. Despite the controversies, these treadmill-induced changes have been accepted by various authors as representative of running investigations [31,32,35]. Regarding local muscle fatigue, the in uence of muscle fatigue on the plantar exors and dorsi exors has been investigated in various publications. However, there is signi cant variability in methodologies, leading to varying muscle activation outcomes. A common limitation is the failure to consider critical factors like foot strike patterns, leg dominance, running speeds, distances, and repeated measurements. Many studies utilize exhaustive running, typically a 30-min run at 85% of the individual's maximal aerobic speed, to induce fatigue [2,10]. However, distinguishing the changes directly resulting from local muscle fatigue remains challenging. The dorsi exors and plantar exors of the foot are highly susceptible to severe fatigue during running, considering their involvement in 50 to 85% of the running cycle [36]. Prior research has indicated that plantar exors experience fatigue after a 2-h running session [37,38]. Similarly, running activities induce signi cant fatigue in the dorsi exors [39,40] despite their primary activity during the swing phase. Notably, the muscular imbalance becomes evident during running with progressive fatigue. The activity of plantar exors remains relatively constant, while that of dorsi exors decreases, resulting in an imbalance [41]. In the domain of kinematics, studies have examined the ankle and knee angles of runners post-fatigue. Kellis and Liassou [36] highlighted that the knee and ankle angles during touch-down play a vital role in joint stability and are particularly crucial during toe-off. Bruggemann et al. [42] observed increased rearfoot angle during touch-down and delayed attainment of its maximum value after fatigue.

the domain of kinematics, studies have examined the ankle and knee angles of runners post-fatigue. Kellis and Liassou [36] highlighted that the knee and ankle angles during touch-down play a vital role in joint stability and are particularly crucial during toe-off. Bruggemann et al. [42] observed increased rearfoot angle during touch-down and delayed attainment of its maximum value after fatigue. Furthermore, Christina et al. [17] observed a decrease in the ankle angle following local muscle fatigue of the dorsi exors, while fatigue of the plantar exors contributed to a notable increase in the ankle angle. Fatigue of the ankle musculature due to movement resulted in a decrease in the dorsi exor angle during the stance phase [36]. A reduced dorsi exor angle signi es that a greater por- tion of the heel has contact with the ground during stance, facilitating enhanced absorption of landing forces [2]. This kinematic adaptation involves an increased knee exor angle [43] and reduced ankle angle during the stance phase [17]. Therefore, the present review and meta-analysis aimed to examine the in uence of general and local muscle fatigue on kinematics and plantar pressure distribution during running. It was assumed that the plantar pressure distribution under the foot would differ according to fatigue protocols; they submitted different results, and this is due to using other fatigue protocols. 2. Materials and Methods 2.1. Study Design and Protocol Registration The present review strictly adhered to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. To maintain accuracy and rigor, dili- gent searches were conducted to identify any errata, corrections, corrigenda, or retrac- tions related to the included studies [44]. Additionally, pre-registered protocols were retrieved when available to uphold transparency and reliability in the review process. To ensure a comprehensive overview, if a study provided supplementary and perti- nent information in another published article, this data was integrated to enhance the completeness of the information. Moreover, the review protocol was registered in the University of York's Centre for Reviews and Dissemination PROSPERO database un- der the registration number CRD42020202711, accessed on 19 September 2020. (http: //www.crd.york.ac.uk/prospero/).

ensure a comprehensive overview, if a study provided supplementary and perti- nent information in another published article, this data was integrated to enhance the completeness of the information. Moreover, the review protocol was registered in the University of York's Centre for Reviews and Dissemination PROSPERO database un- der the registration number CRD42020202711, accessed on 19 September 2020. (http: //www.crd.york.ac.uk/prospero/).

Sports2023,11, 241 4 of 27 2.2. Inclusion and Exclusion Criteria Inclusion and exclusion criteria were established following the participants, exposure, comparator, outcome, and study design (PECOS) framework. Inclusion criteria encom- passed cross-sectional studies published in peer-reviewed journals focused on fatigue and plantar pressure distribution during treadmill running. Studies that delved into plantar pressure distribution, running biomechanics (including kinematics, kinetics, and EMG outcomes), and temporospatial parameters involving healthy adult runners were consid- ered. On the other hand, exclusion criteria comprised studies reporting on individuals with preexisting medical pathologies such as diabetes, neuromuscular, or cardiovascular diseases. A comprehensive overview of the eligibility criteria can be found in (Table). Table 1.Eligibility Criteria. Criterion Description Type of participant Healthy adult runners (all competitive levels, all sexes). Type of comparison Effect analysis (fatigue by jumping, fatigue by running, and local muscle fatigue) or regression analysis (running biomechanics). Type of outcome measure Plantar pressure distribution, running biomechanics (kinematics, kinetics, and EMG outcomes), temporal-spatial data Type of Study cross-sectional studies will be included Publication status Peer-reviewed journal publication Publication date The included studies were not restricted to a speci c date of publication. Language of publication English or German language 2.3. Search Strategy Initial searches were conducted in PubMed (1950 to 30 November 2021, and updated on 29 April 2023), The Cochrane Library (1991 to 30 November 2021, and updated on 29 April 2023), SPORTDiscus (1977 to 30 November 2021, and updated on 29 April 2023), and Web of Science (Thomson Reuters, New York, NY, USA) (1945 to 30 November 2021, and updated on 29 April 2023), without restrictions on publication date and no lters applied. Subject headings, synonyms, relevant terms, and variant spellings for the searches on each database were used. Manual searches were conducted by screening the included studies and relevant review reference lists. The general search strategy used the following free terms without lters or limits applied: The complete eligibility criteria are listed in Table. We used the following keywords: (“run” OR “running” OR “jump”) AND (“fatigue” OR “exhaust” OR “tired” OR “exert” OR “prolong”) AND (“biomechanics” OR “kinematic” OR “kinetic” OR “ground reaction

screening the included studies and relevant review reference lists. The general search strategy used the following free terms without lters or limits applied: The complete eligibility criteria are listed in Table. We used the following keywords: (“run” OR “running” OR “jump”) AND (“fatigue” OR “exhaust” OR “tired” OR “exert” OR “prolong”) AND (“biomechanics” OR “kinematic” OR “kinetic” OR “ground reaction force” OR “electromyography” OR “plantar pressure”). Primarily, the databases were searched to prepare a list of functional studies based on the article title and abstract. Prospective snowballing citation tracking was performed in Web of Science on 17 December 2021 and updated on 29 April 2023. 2.4. Study Selection Two independent reviewers (W.H. and M.A.) conducted the initial identi cation of relevant studies, with a third reviewer (K.M.) available for consensus in cases of disagree- ment. The identi ed studies were initially screened against the inclusion criteria, beginning with a title evaluation, then an abstract assessment, and nally, a thorough review of the full text. Furthermore, the bibliographical information of the included articles was meticu- lously examined to identify additional relevant references. Citation tracking was executed using the Web of Science (Thomson Reuters). For inclusion in this review, articles had to meet speci c criteria, including cross-sectional studies published in peer-reviewed journals

Sports2023,11, 241 5 of 27 written in English or German. Conversely, reviews, systematic reviews, commentaries, case studies, and case series were excluded from the review process. 2.5. Data Extraction Two independent reviewers (W.H. and M.A.) conducted the data collection, utilizing two separate Excel sheets: (1) baseline summary comprising study ID, title, country, study design, sample size, inclusion criteria, aim, primary outcome, secondary outcome, and conclusions; and (2) speci c biomechanical data encompassing stride frequency, stride length, maximum pressure under the heel, maximum pressure under the metatarsus, and maximum pressure under the forefoot for both the right and left forefoot and rearfoot after local muscle fatigue. Notably, the data presented in this review primarily pertains to a running velocity of 15 km/h, as no signi cant differences were observed in the results for other velocities. In cases where data was missing, the authors of the included studies were promptly contacted to request the necessary information. 2.6. Quality Assessment The risk of bias within the included studies was independently assessed by two reviewers (WH and MA) using the Joanna Briggs Institute (JBI) critical appraisal checklist for cross-sectional studies [45]. Each question in the checklist was evaluated as either “Yes,” indicating a low risk of bias, “No”, indicating a high risk of bias, “Unclear”, or “Not applicable”. To enhance the transparency and clarity of the risk-of-bias assessment, the Risk-of-bias Visualization (robvis) software was employed to visualize the appraisal outcomes [46]. 2.7. Statistical Analysis The statistical analysis used Review Manager (RevMan) software version 5.4. Results with ap-value (P) less than 0.05 were considered statistically signi cant in the Z-test. The meta-analysis results for continuous outcomes were presented using mean difference (MD) and a 95% con dence interval (CI). For the analysis, the xed-effect model was utilized. To assess heterogeneity among the studies, the Chi-square test was employed to measure its signi cance. Potentially signi cant heterogeneity was de ned if thep-value was less than 0.1. Furthermore, the degree of heterogeneity was evaluated using the I 2 test [47]. The I 2 statistic ranges from 0% to 100%, indicating low heterogeneity (25%), medium heterogeneity (50%),

was utilized. To assess heterogeneity among the studies, the Chi-square test was employed to measure its signi cance. Potentially signi cant heterogeneity was de ned if thep-value was less than 0.1. Furthermore, the degree of heterogeneity was evaluated using the I 2 test [47]. The I 2 statistic ranges from 0% to 100%, indicating low heterogeneity (25%), medium heterogeneity (50%), and high heterogeneity (75% or greater) [48]. This statistic gauges the extent of inconsistency across studies in a meta-analysis, providing valuable insights into result consistency. Notably, the I 2 statistic can be directly compared between meta-analyses involving different numbers of studies and various types of outcome data. It is considered preferable to a test for heterogeneity in assessing the consistency of evidence [49]. 3. Results The literature search yielded a total of 6626 records. After removing 2000 duplications through automated processes using EndNote™20.2 for Mac (Clarivate™) and subsequent manual screening, 4626 studies remained for the title and abstract screening. Following the title and abstract screening, 201 articles were selected for full-text screening. Eventually, 20 studies met the criteria for inclusion in our qualitative data synthesis, and among them, three studies were included in our meta-analysis (Figure).

This systematic review examines how muscle fatigue affects running biomechanics.