Association of GPS Metrics with Explosive Lower Limb Power and Their Relationship with Post-Competition Neuromuscular Fatigue in Professional Soccer Players

Abstract

This study aims to examine the relationship between competition-derived GPS metrics and explosive power, as expressed by the countermovement jump (CMJ), and their influence on neuromuscular fatigue in professional male soccer players. In this observational–longitudinal study, GPS-derived data were collected during 15 official competitions from the same seven players (age = 26.03 ± 4.59 y, height = 180.0 ± 0.076 cm, body mass = 77.88 ± 9.90 kg). CMJ assessments were performed at matchday − 1 (MD + 2) and matchday + 2 (MD + 2) of each competition. CMJ height was significantly decreased from MD − 1 to MD + 2 (p < 0.05). While no significant correlations were found between MD − 1 CMJ values and the examined GPS metrics (total distance covered (TDC), high-speed running distance (HSR-D (m)), sprint-running distance (SR-D (m)), and number of high-intensity accelerations/decelerations (HIA (n)/HID (n), respectively), a significant negative relationship emerged between MD + 2 CMJ height and HIA (n) and HID (n) (p < 0.05). Linear mixed-effects measures revealed the impact of several parameters in three different models: (a) HIA (n) × HID (n) × HSR (m) × SR-D (m), (b) HIA (n) × HID (n) × SR-D (m), and (c) HID (n) × SR-D (m), with univariate testing highlighting significant effects of HIA (n) and HID (n) (p < 0.05). In conclusion, no association was evident between MD − 1 CMJ values and competition GPS metrics, while HIA (n) and DIA (n) were associated with post-competition explosive-power values at MD + 2. Moreover, CMJ reduction from MD − 1 to MD + 2, serving as a competition-induced neuromuscular fatigue indicator, was found to be related to HIA (n) and HID (n) volumes either individually or in association with HSR (m) and SR-D (m) distances, suggesting those to impact post-competition fatigue kinetics.

1. Introduction

In the past decade, an evolutionary progression of the soccer competition workload profile towards higher intensity and volume has been observed [1]. The increase in competitive game demands as well as the training environment has led to greater needs for fatigue-related monitoring and assessment within the game [2] and the quantification and analyses of the physical loads players are exposed to during competitive matches [1]. Within elite-level soccer, this increased intensified environment has been suggested to be highly related to high levels of neuromuscular fatiguing activities on a cyclical basis [3], and specific investigations have demonstrated that neuromuscular status as expressed by strength, power, and subsequent derivatives has been linked with the most decisive soccer actions within competition [4]. Furthermore, it has been suggested that competition-induced neuromuscular fatigue levels can be revealed through direct relations of monitored neuromuscular fitness indices [1,5]. In addition, recent evidence [6] indicates that laboratory-based fitness indices have been associated with global positioning system (GPS) pitch-based training outputs amongst Champions League players. The latter further highlights the need for future research examining the possible association of specific GPS-derived match-play activities that could serve as potential indicators of both neuromuscular performance and fatigue levels, providing guidance for the right distribution and management of the training load [7].

To date, a reliable and accurate method of measuring both neuromuscular status and fatigue amongst elite athletes is countermovement jump (CMJ) [8]. CMJ has been commonly used within athletic performance settings, including soccer, to assess lower limb dynamic neuromuscular performance capabilities [9,10]. As a monitoring tool, it has been suggested to be one of the most accurate field tests for the determination of explosive power of the lower limbs [11], and a plethora of evidence is highlighting the existence of a linear relationship between CMJ performance, high-intensity actions, and explosive-type human movements that occur during a competition [12]. In addition, CMJ has been suggested to serve extremely well as an objective indicator of readiness to compete and to be associated with the identification of performance adaptations [13,14]. Further findings have reported a relationship between CMJ and post-competition residual fatigue, further verifying CMJ as a suitable tool for the monitoring of neuromuscular fatigue [15,16].

Regarding competition load quantification and management, GPS technology has evolved as a standard tool assisting coaches and sports scientists for monitoring match-play external loads across a range of training and competitive levels [17]. This monitoring methodology has been determining the conditioning needs of the players in order to serve as a guide for the training process [18], supporting the primary goal of load monitoring, which is to assist the coaches’ decision-making process for the necessary training load modifications in order to avoid inappropriate stimulus during the weekly microcycle [6]. Amongst the recent literature in this area, the most commonly explored metrics through GPS during competition include total distance covered (TDC), number of high-intensity accelerations (HIA (n)) and decelerations (HID (n)), high-speed running distance (HSR-D), and sprint-running distance (SP-D) [19].

Due to the suggested properties of CMJ, constituting it a multi-informative screening tool [11,12,14,17], this could provide huge benefits to applied practitioners, allowing individual adjustments to training programs, minimizing injury risk, restoring players’ physical performance, and informing practitioners further of the recovery process [20]. Although some attempts have been made in this direction, this is a topic of limited research at the elite level [6]. Regarding players’ post-match fatigue-related responses, a limited number of studies have examined the association of CMJ as an indicator of neuromuscular fatigue with competition external load metrics specifically in soccer [20]. That evidence has reported a trivial to small relationship of TDC with CMJ values, although the majority of the available literature fails to report such an association [20]. Regarding the HIA (n), HID (n), and HSR-D, but not HS-D, there is some evidence implicating those with residual post-competition neuromuscular fatigue [1,6,20,21]. Notably, these suggestions are limited, mainly examining CMJ peak-power output (PPO) and not jump height, which has been widely used by the majority of the studies examining its association with neuromuscular fatigue [3,11,22]. Furthermore, a controversy is evident regarding whether the suggested HIA (n), HID (n), and HSR-D induced residual fatigue, as quantified by CMJ, persists for more than 24 h post-competition [20]. According to the available literature, this association at 48 post-match play has been rated as low and moderate for HID (n) and HIA (n), respectively, whilst conflicting evidence exists for HSR-D [20].

Even less evidence exists for the association of physical capabilities, including CMJ as a measure of strength and power, and external load metrics. The majority of the limited literature has observed a link of several GPS metrics with either endurance- or speed-related indices [23] but not strength and power. Regarding CMJ, to the best of the authors’ knowledge, only one recent study has examined its association with GPS physical outputs during soccer training sessions, revealing a linear relationship with high-intensity-related metrics, including acceleration and deceleration number and high-speed running distance, but not with TDC [6], whilst no evidence exists for sprint distance. Notably, although GPS has not been developed for the determination of strength and power levels of the athletes, it is well demonstrated that high-intensity efforts such as accelerations, decelerations, and high-speed and sprint running that are repeatedly observed during a soccer competition can be limited by their development [1,12], indicating an indirect relationship between those external load measures and strength and power derivatives.

In summary, there seems to be a paucity of literature examining the association between the most commonly examined GPS metrics during competitions and CMJ height at different time points within the in-season training process and specifically in MD − 1 and MD + 2, and, furthermore, whether those metrics could have an impact on neuromuscular fatigue magnitude. Therefore, the aims of the current study were (a) to examine whether CMJ pre-competition levels (match day − 1 [MD − 1]), as a measure of power and indicator of readiness to compete, would be related with TDC, HIA (n), HID (n), HSR-D, and SP-D, and if these metrics would affect lower extremities explosive power levels (as measured by MD + 2 CMJ), and (b) whether these match-day outputs could be associated with the magnitude of competition-induced neuromuscular residual fatigue. Our working hypothesis was that an association would be evident with all examined GPS metrics with MD − 1, whilst only HIA (n) and HID (n) would be related to changes in MD + 2 CMJ values and, furthermore, would have an impact on residual neuromuscular fatigue magnitude.

2. Materials and Methods

2.1. Study Design and Participants

The duration of this observational longitudinal study was that of the competition season. Throughout this period, data collection for analyses was employed according to the following criteria: (i) weekly microcycles situated within a 1-game week, 6 days apart from the previous competition, and under the same structure. In particular, in each of these weeks players typically participated in five training sessions scheduled on the same days (i.e., match day [MD], plus [+], or minus [−]; MD + 2, MD − 4, MD − 3, MD − 2, and MD − 1), while MD + 1 was a day off, an approach that has been commonly employed in professional soccer [13]. (ii) The forthcoming (post-competition) week to be of similar structure or following at least the same pattern for the first two post-competition sessions, i.e., day off at MD + 1 and the 1st training session of the week at MD + 2, and (iii) training sessions during MD − 1 and MD + 2 that were held at the same time of day (morning for MD − 1 and 48-h post-competition for MD + 2) to limit the effects of circadian variation on CMJ values. Altogether fourteen (n = 14) separate microcycles were found to fulfill those criteria, and fifteen (n = 15) official competitions were employed in this study.

In order for players to participate in this study, they had to be included in the selection squad of these 15 competitions and they had to fulfill the following criteria: (a) to be chosen as starters; (b) to participate in the whole competition (full time and extra time); (c) to participate in the full number of training session of the specific weekly microcycles included in this study (i.e., their absence from any weekly session or sessions due to musculoskeletal and neurological pathologies such muscle or tendon strain and joint or ligament sprains or overuse injury related issues or any other factors); (d) to participate in all the performed CMJ testing; and (e) to have participated in every single of the competitions examined, fulfilling criteria a, b, c, and d, in order to have exactly the same individuals for analyses during each one of the 15 experimental periods. From a total pool of twenty-five in-field professional male soccer players who were members of a Greek Superleague Team, seven (n = 7) players fulfilled the inclusion criteria in all 15 competitions and were included in this study. All players provided written informed consent in accordance with the ethical guidelines of the Helsinki Declaration. Data were obtained from the football club as the players were daily monitored, throughout the whole season, for training load monitoring purposes. Therefore, ethics committee clearance, as is usually performed in research procedures, was not required [24]. Nevertheless, the study protocol was reviewed by the responsible institutional ethics committee, which granted an exemption from ethical approval. In addition, in order to ensure player and team confidentiality, prior to the analyses, all obtained data were anonymized, and the research was conducted in accordance with the Declaration of Helsinki.

2.2. Procedures

2.2.1. Anthropometry

Height was measured using a stadiometer (Charder HM210D, Charder Electronics CO, LTD, Taichung City, Taiwan), weight was obtained using an electronic weight scale (Seca Alpha 770, Seca Vogel, Hamburg, Germany), and body-fat percentage was assessed by skinfold thickness measurement (Lange Skinfold Caliper, Cambridge Scientific Instruments, Cambridge, UK) using the 4-site formula proposed by Durnin and Womersley [25].

2.2.2. Countermovement Jump Assessment

CMJ height (cm) was assessed with a jumping mat (Powertimer, Newtest Ltd., Oulu, Finland) according to standard procedures [11]. Players were familiarized with these procedures, as they had been repeatedly tested throughout the previous season. The test–retest reliability of this jump height assessment was found to be of acceptable levels (coefficient of variation [CV] = 8.09%; intraclass correlation coefficient [ICC] = 0.82).

2.2.3. GPS Data Collection

Player’s outputs were collected by GPS technology (Catapult S5, Melbourne, Australia) with a sampling frequency of 10 Hz, a system that has been shown to be a valid and reliable assessment marker for monitoring team-sport movement demands [26]. For the purposes of the current investigation, the following variables were assessed: total distance covered in meters [TDC (m)], high-speed running distance in meters [HSR-D (m); (>19.8 km/h)], sprint-running distance in meters [SR-D (m); (>25.5 km/h)], high-intensity accelerations number [HIA (n); (>2.5 m/s²)], and high-intensity decelerations number [HID (n); (<−2.5 m/s²)]. GPS devices were activated according to the manufacturer’s guidelines prior to the warm-up, and in order to avoid inter-unit error, each player wore the same GPS device throughout this study [27]. Following each competition, GPS data were downloaded using the respective software package for analyses (Openfield v1.14, Catapult Sports, Melbourne, Australia).

2.3. Statistical Analyses

Statistical analysis was performed using the software program SPSS 21.0 (SPSS Inc., Chicago, IL, USA). Results are presented as means ± SD. Player characteristics were as follows: mean age 26.03 ± 4.59 years, height 180.0 ± 0.076 cm, and body mass 77.88 ± 9.90 kg. The changes between MD − 1 and MD + 2 CMJ height were analyzed by the paired samples t-test. Effect sizes (ES) were calculated to determine the magnitude of changes between MD − 1 and MD + 2 CMJ height as proposed by Cohen [28]: values of 0 to <0.20, 0.20 to <0.50, 0.50 to <0.80, and >0.80 were considered to represent trivial, small, medium, and large differences, respectively. The distribution of variables was tested by the Shapiro–Wilk statistical method. Then, Pearson’s (for normally distributed variables) and Spearman’s (for non-normally distributed variables) correlation coefficients were used to assess the linear relationship between CMJ height (cm) values in MD − 1 and MD + 2 with total distance covered TDC (m), HSR-D (m), SR-D (m), HIA (n), and HID (n). The correlations were distributed according to R-values, which were classified as very weak (0.0–0.2), weak (0.2–0.4), moderate (0.4–0.7), strong (0.7–0.9), and very strong (0.9–1.0) [29].

Linear mixed-effects measures for modeling the effects of time, TDC (m), HSR-D (m), SR-D (m), HIA (n), and HID (n), with dependent variables being the CMJ pre- and CMJ post-competition values’and independent variables being the day of observation (1, 2), and the aforementioned GPS metrics were used to assess CMJ change over time. The level of significance was set at p < 0.05.

3. Results

A statistically moderate-level significant decrease was observed in CMJ values from MD − 1 to MD + 2 (p < 0.001; d = 0.76) (Figure 1). Analyses of our data failed to observe any association between CMJ MD − 1 height and TDC (m) (p = 0.69 > 0.05; r = −0.182), HSR-D (m) (p = 0.482 > 0.05; r = 0.71), SR-D (m) (p = 0.389 > 0.05; r = 0.87), HIA (n) (m/s²) (p = 515 > 0.05; r = 0.65), and HID (n) (m/s²) (p = 793 > 0.05; r = 0.26) (

Table 1. Correlations (correlation coefficients (p values)) between MD − 1 CMJ and MD + 2 CMJ height (cm) values with competition GPS-derived metrics.

GPS Metrics	TDC (m)	HSR-D (m)	SR-D (m)	HIA (n)	HID (n)
MD − 1 CMJ values	−0.163 (0.96)	0.73 (0.46)	0.10 (0.29)	0.082 (0.40)	0.040 (0.684)
MD + 2 CMJ values	−0.182 (0.06)	0.61 (0.53)	0.51 (0.60)	−0.301 * (0.002)	−0.317 * (0.001)

(*) indicates significant correlation at the level of significance p < 0.05.

).

A significant weak negative association with both HIA (n) (p = 0.01 < 0.05; r = 0.315), and HID (n) (p = 0.01 < 0.05; r = 0.325) with MD + 2 CMJ height was evident (Table 1). No significant relationships were observed between CMJ MD + 2 with either TDC (p = 0.051 > 0.05; r = −0.195), or HSR-D (p = 0.468 > 0.05; r = 0.73) and SR-D (p = 0.560 > 0.05; r = 0.59).

Statistically significant mixed-effects models for CMJ change over time were observed in three models (

Table 2. Linear mixed-effects measures for modeling the effects of time, HIA (n).

Within-Subjects Effects
	Sum of Squares	df	Mean Square	F	p-Value
Model 1: Time × HIA (n) × HID (n) × HSR-D (m) × SR-D (m)	2.173	1	2.173	5.767	0.01 *
Model 2: Time × HIA (n) × HID (n) × SR-D (m)	1.914	1	1.914	5.080	0.02 *
Model 3: Time × HID (n) × HSR-D (m)	1.895	1	1.895	5.029	0.02 *
# Model 4: Time × HIA (n)	2.127	1	2.127	2.532	0.04 *
# Model 5: Time × HID (n)	1.893	1	1.893	4.378	0.01 *

(^#) Univariate testing of HIA (n) and HID (n) revealed statistically significant impact, with F = 2.532, p-value = 0.04 and F = 4.378, p-value = 0.01, respectively. (*) indicates a significant effect at the level of significance p < 0.05.

). In model 1, it is observed that time, HIA (n), HID (n), HSR-D (m), and SR-D (m) are contributing to CMJ change (mean square = 2.173, F = 5.767, p = 0.01). In model 2, time, HIA (n), HID (n), and sprint running are still presenting a significant effect (mean square = 1.914, F = 5.08, p = 0.02), and in model 3, only time, HID (n), and HSR-D (m) are associated with CMJ change (mean square = 1.895, F = 5.029, p = 0.02). Additionally, univariate testing of HIA (n) (model 4) and HID (n) (model 5) revealed statistically significant impact, with F = 2.532, p = 0.04 and F = 4.378, p = 0.01, respectively.

4. Discussion

The aim of the current study was to examine the association of specific competition-derived GPS metrics with explosive lower limb power, as expressed by CMJ, and the possible impact of those metrics on post-competition neuromuscular fatigue levels in professional soccer players. Our findings revealed that none of the examined match-play outputs were related to MD − 1 explosive power levels since no association was evident between their outputs and MD − 1 CMJ values. Among the examined metrics, only HIA (n) and HID (n) were found to have a significant negative association with MD − 2 CMJ height.

Implicating their outputs with the significant observed decline in explosive power performance at MD − 2. In support of our hypotheses, HIA (n) and HID (n) were found to have an impact on the competition-induced neuromuscular fatigue magnitude, as expressed by the level of CMJ performance deterioration from MD − 1 to MD − 2. In addition, our analyses further revealed that the combination of (a) HIA (n), HID (n), HSR-D (m), and SR-D (m) volume; (b) HIA (n), HID (n), and SR-D (m) volume; and (c) HID (n) and HSR-D (m) volume was associated with the significant observed CMJ change over time.

To the best of our knowledge, this is the first study examining in professional soccer whether MD − 1 CMJ height values as measures of power and an indicator of readiness to compete could be related with the forthcoming competition TDC, HIA (n), HID (n), HSR-D (m), and SR-D (m) outputs. In contrast to our hypothesis, no association was evident between MD − 1 CMJ values and any of the examined GPS metrics. Our experimental rationale under this hypothesis was based on the widely proposed profound properties that CMJ as a diagnostic tool has been suggested to provide. More specifically, it was based on the suggestions constituting CMJ as a sensitive indicator of neuromuscular fatigue [1]. The readiness to compete [13,14] and the well-supported association of its levels with strength and power performance, which are well-demonstrated parameters affecting accelerations, decelerations, and high-intensity and speed actions [14,15,16]. Therefore, based on the aforementioned evidence, it was speculated that MD − 1 CMJ values could indicate either the presence of neuromuscular fatigue or enhanced readiness to compete and optimum explosive power levels that could, in turn, result in an analogous proportional effect on the examined locomotor outcomes of the forthcoming competition [30]. However, the lack of an observed association deconstructs the aforementioned hypotheses. Supporting evidence for the observed lack of an association between MD − 1 CMJ values and the examined competition GPS metrics is provided by the suggestion that no definitive evidence exists to support that incomplete recovery and therefore reduced readiness to compete actually results in decreased running performance in ensuing match-play [5]. Furthermore, a compilation of research has suggested that a range of contextual, tactical, mental, and fatigue-related factors have a meaningful impact on players’ activity profiles during a competitive game [1,5]. Those include, amongst others, competition demands, strength and opposition quality, playing formation, style of play, match flow score, match location, environmental factors, competition importance, mentally sustained concentration and fatigue, perceptual ability, and decision-making [31,32,33,34]. Therefore, the suggestion of the aforementioned evidence indicating that match running performance is highly dependent on the integration of all these factors could further justify the lack of an association between MD − 1 CMJ levels and the examined competition external load outputs in our study.

In accordance with the available literature [5,16,21,35], a significant decline in lower extremities explosive power was evident at MD − 2, as indicated by the reduction in CMJ height. This observation is in accordance with the well-documented findings reporting that several aspects of the capacity to generate strength and power are compromised after match play [36] and that this is a persistent effect [1,16]. Our observed retained decline in power at MD + 2 is well in line with the time frame reported in the available literature, revealing long-lasting effects for a period from 24 up to 72 h post-competition, although these findings are not universal [5,16,20]. Some authors have failed to report a residual effect of soccer match-play on CMJ [20], whilst others reveal that this reduction was reversed at MD + 2, suggesting that this period of time was sufficient for recovery [37]. These discrepancies could have been accounted for by different methodological approaches, the varying characteristics of the population used (i.e., age, sex, and individual athlete characteristics), and even the type of CMJ indices employed in the analyses. Regarding the latter, several CMJ metrics have been examined, including average height, peak and mean power, peak and mean force, and flight time/contraction [38]. The various outcomes of the studies examining these different CMJ indices have designated the sensitivity of CMJ height to be a subject of debate [38]. However, our findings are contrasting the observations, limiting the value of jump height as a monitoring tool for power decrements and residual fatigue [39]. According to our results, it could be suggested that CMJ values, and, in particular, height, could serve as a sensitive and reliable indicator to accurately discern athlete residual neuromuscular fatigue status and the neuromuscular performance decline at MD + 2 in professional soccer players in support of the widely accepted property of CMJ serving as an indicator of neuromuscular fatigue in addition to lower limb explosive power [1,7,20]. This suggestion is further supported by the observation that this prolonged affected expression of power is highly dictated by monitoring activities that include the stretch shortening cycle (SSC), such as CMJ [16,40]. Furthermore, since soccer match play involves many SSC actions, and SSC recruitment has been previously highly implicated with power deterioration and residual exercise fatigue [41], our findings are indicating CMJ height to constitute an important monitoring tool of neuromuscular status in this specific sporting discipline.

The aforementioned significant decline in power post-competition, as indicated by reduced CMJ values at MD + 2, was negatively associated with HIA (n) and HID (n) but not with any of the TDC, HSR-D (m), and SR-D (m). This observed weak negative association of HIA (n) and HID (n) with MD + 2 CMJ values is comparable with the reports showing that despite the contrasting evidence on the correlation strength between match HIA (n) and HID (n) with MD + 2 CMJ values, a consistent effect, even of a small magnitude, is evident [5,20,21]. The mechanisms underpinning those findings have been previously described in the literature. Competition HIA (n) and HID (n) profiles have been found to be associated with the inflammatory process related to muscle damage and repair, resulting in hindered neuromuscular performance for a period even up to 72 h post-competition [41]. Regarding HSR-D (m), in contrast to our findings, there is some evidence implicating its competition output as being a sensitive informative tool in this monitoring process, suggesting that this metric should be considered as a reliable indicator of neuromuscular status [16,20]. However, this reported association has been found to be limited to periods up to 24 h post-competition and not at MD + 2 as in our study [20,21]. Furthermore, the reported moderate associations between HSR-D (m) and neuromuscular performance deterioration at MD + 2 have been related to its relative values and not the absolute ones that were employed in the current study, as well as with CMJ peak power output and not jump height [20]. Lastly, the finding that neither TDC nor SP-D (m) was associated with the power decline and residual neuromuscular fatigue at MD + 2 is in agreement with the outcomes of recent well-structured literature reviews revealing that these measures cannot reflect the observed reduction in MD − 2 CMJ values and, therefore, do not constitute sensitive variables to monitor neuromuscular status alterations [16,20].

In support of our hypotheses, both HIA (n) and HID (n) were found to have an impact on neuromuscular fatigue levels, as they were observed to be contributors to CMJ level changes over time, from MD − 1 to MD − 2. This finding is in accordance with the observation that HIA (n) and HID (n) volume may affect post-match recovery kinetics [42]. The importance of this suggestive dose–response relationship relies on the fact that, to date, to the best of our knowledge, no studies in soccer have examined the possible dose–response relationship of specific external load metrics in terms of being related to post-competition residual neuromuscular fatigue magnitude [20]. These observed effects of both HIA (n) and HID (n) are indicating that residual neuromuscular fatigue is vulnerable to intense accelerations and decelerations, and moreover, that the magnitude/volume of those external load outputs during each specific competition would in turn affect CMJ MD + 2 values and therefore could impact CMJ change from MD − 1 to MD + 2 proportionally and in an opposite manner. Regarding TDC HSR-D (m) and SR-D (m), the failure to observe any significant impact on CMJ performance alterations is supported by the observation that those metrics do not reflect the competition-induced neuromuscular fatigue changes at MD + 2 [20], a suggestion further supported by the findings of the current study. The observed significant impact of the recorded (a) HIA (n), HID (n), HSR-D (m), and SR-D (m) volume; (b) HIA (n), HID (n), and SR-D (m) volume; and (c) HID (n) and HSR-D (m) volume was most probably a main effect of the HIA (n) and HID (n) outputs combined with those metrics. In any case, those models could also serve as tools in the process of fatigue monitoring and training load.

In summary, our findings suggest that MD − 1 CMJ values are not associated with any of the examined match-play outputs and therefore do not affect the competition-derived outputs of these metrics. HIA (n) and HID (n) outputs, but not TDC, HSR-D (m), and SR-D (m), were found to be related to the observed decline in power, as expressed by CMJ height values, at MD + 2. The latter findings, in conjunction with the observation that only HIA (n) and HID (n) were found to be related with the observed CMJ change over time at MD − 2, are highlighting the significant role that those specific two metrics play on the competition-induced residual neuromuscular fatigue levels, justifying their employment as sensitive measures of residual fatigue in professional soccer players. It should be mentioned that the current study is subject to specific limitations. Firstly, the low number of participants is a significant limitation of our study, not allowing for a broad generalization of our findings. However, despite this low number of participants, the actual nature of the sport itself, where even five players can be substituted in the competitions, reducing the number of those participating in the whole match-play to five, provides a strong rationale for evaluating the study observation with consideration. Another limitation worth mentioning is the lack of control over several contextual factors, such as, but not limited to, home or away competitions, opponent level, and travel, that could be related to inter-match variability in fatigue responses and that could provide further justification for our findings. Further research with a larger number of participants and controlling several fatigue-related contextual factors should be performed to confirm these observations across the same type of populations.

5. Conclusions

Our findings are providing further evidence to support the employment of CMJ height as a reliable and sensitive tool for monitoring long-lasting post-competition alterations in the neuromuscular status of professional soccer players within the weekly microcycle. Furthermore, according to our results, the level of this alteration in neuromuscular status, which is indicative of post-competition residual neuromuscular fatigue, can be partially quantified mainly by both HIA (n) and HID (n). This finding could be of benefit to applied practitioners seeking methods guiding the right distribution and management of the training load the days following competitive encounters.