VO2max = 36.4 + (0.0084 × covered distance in YYIRT-level 1)

Training Interventions. The training procedure is summarised in Table 1. During the 6-week training period, young players performed 2 combined training sessions (SSGs + HIIT or HIIT + SSGs) a week in addition to their 3 days of soccer-specific training. Their weekly training routine consisted of 5 60–75 min practice sessions and 1 soccer match. During the study, their coach generally focused on developing core strength and technical and tactical skills, except for the 2 combined training sessions. After 15 min of standardised warmup, which consisted of jogging and dynamic stretching at each training session, players performed combined training, including SSGs + HIIT or HIIT + SSGs. A gradual progress plan was designed to reach maximal final performance in combined training programmes. Players performed 2, 3, and 4-a-side formats of SSGs, including free game, possession, and small goal for two 4–16 min games per training session according to the procedures detailed by Sanchez-Sanchez et al. [29]. Verbal encouragements were given by coaches throughout the SSGs. Players performed HIIT sessions, which consisted of 15 s of intermittent running at 90–100% of players' velocity at IFT (VIFT), followed by 15 s of resting (Table 1).


**Table 1.** Description of the 6 weeks of combined training programs.

FG: free game; POS: possession; SG: small goal; VIFT: Maximum speed reached in the last stage of the 30-15 Intermittent Fitness Test.

The rating of perceived exertion (RPE) was obtained using the category ratio scale (6–20) to calculate the internal training load (ITL) immediately after the completion of each session [30]. The scale was introduced at the beginning in order to familiarise the players. All players also completed a short form of the physical activity enjoyment scale (PACES). This scale includes 5 items scored on a 1–7 Likert scale and has been validated [31] as a marker of enjoyment level for physical activity by Turkish youth [1].

#### *2.4. Statistical Analyses*

Data were expressed as mean ± standard deviation (SD). Group differences in psychophysiological responses, in terms of RPE, PACES, and ITL (overall) results between SSGs + HIIT and HIIT + SSGs, were assessed using the independent sample *t*-test. A mixed ANOVA was used to test for interactions and main effects for time (pre- vs. post-test) and group (SSGs + HIIT vs. HIIT + SSGs) on the physical and technical performances. Effect sizes (Cohen's *d*) were also calculated for each dependent variable. Cohen's *d* values were considered trivial (<0.20), small (0.20–0.59), moderate (0.6–1.19), large (1.2–1.99), and very large (≥2.0) [32]. All statistical analyses were computed using SPSS version 24.0 (SPSS, Version 24.0 for Windows; SPSS Inc., Chicago, IL, USA). Statistical significance was set at the level of *p* ≤ 0.05.

#### **3. Results**

Pre-test values and the effect of combined training on the body composition, physical performance responses, and technical skills of the players are summarised in Table 2.


\* *p* ≤ 0.05 for within-group changes.

Both combined training interventions (SSGs + HIIT and HIIT + SSGs) showed similar improvements in body composition, physical performance responses, and technical skills (*p* ≥ 0.05, *d* values ranging from 0.40 to 1.10) (Table 2) (Figure 1).

VO2max (ml.min-1.kg-1)

20-m (s) 3.06 ± 0.11 2.95 ± 0.10\* -0.11 3.05 ± 0.20 2.94 ± 0.21\* -0.11 0.048 0.829 0.002

30-m (s) 4.42 ± 0.09 4.19 ± 0.08\* -0.23 4.34 ± 0.26 4.14 ± 0.23\* -0.20 0.861 0.364 0.038

CMJ (cm) 31.72 ± 2.70 33.98 ± 2.44\* 2.26 32.01 ± 2.10 33.90 ± 1.89\* 1.89 0.013 0.911 0.001

ZAWB (s) 8.44 ± 0.32 8.28 ± 0.31\* -0.16 8.60 ± 0.23 8.40 ± 0.31\* -0.20 1.479 0.237 0.063

ZAWOB (s) 6.92 ± 0.23 6.79 ± 0.23\* -0.13 6.79 ± 0.36 6.66 ± 0.37\* -0.13 1.083 0.309 0.047

RSAtotal (s) 39.08 ± 1.01 37.55 ± 0.93\* -1.53 38.68 ± 1.08 37.09 ± 0.73\* -1.59 1.297 0.267 0.056

SDA (s) 25.90 ± 1.47 24.94 ± 1.49\* -0.96 25.00 ± 1.53 24.09 ± 1.39\* -0.91 2.113 0.160 0.088

TCRT (s) 28.63 ± 0.47 25.01 ± 0.95\* -3.62 28.32 ± 1.10 25.14 ± 0.98\* -3.16 0.066 0.800 0.003

YYIRTL-1 (m) 1248.3 ± 107.7 1393.0 ± 107.1\* 144. 7 1213.3 ± 95.5 1363.3 ± 87.7\* 150.0 0.816 0.376 0.036

(*p* ≥ 0.05, *d* values ranging from 0.40 to 1.10) (Table 2) (Figure 1).

46.89 ± 0.90 48.10 ± 0.90\* 1.21 46.59 ± 0.80 47.85 ± 0.74\* 1.26 0.816 0.376 0.036

Both combined training interventions (SSGs + HIIT and HIIT + SSGs) showed similar

**Figure 1.** Improvement in body composition, physical and technical performance responses following the combined training interventions. **Figure 1.** Improvement in body composition, physical and technical performance responses following the combined training interventions.

Overall RPE responses to HIIT + SSGs training were meaningfully lower than those from the SSGs + HIIT group (16.2 ± 0.5 vs. 17.6 ± 0.5; *p* = 0.00, *d* = 2.98). Moreover, overall PACES scores from the HIIT + SSGs training were meaningfully greater than those from the SSGs + HIIT group (30.7 ± 1.1 vs. 26.3 ± 0.9; *p* = 0.00, *d* = 4.28). Conversely, the SSGs + Overall RPE responses to HIIT + SSGs training were meaningfully lower than those from the SSGs + HIIT group (16.2 ± 0.5 vs. 17.6 ± 0.5; *p* = 0.00, *d* = 2.98). Moreover, overall PACES scores from the HIIT + SSGs training were meaningfully greater than those from the SSGs + HIIT group (30.7 ± 1.1 vs. 26.3 ± 0.9; *p* = 0.00, *d* = 4.28). Conversely, the SSGs + HIIT group demonstrated a higher training load than those from the HIIT + SSGs group for all weeks (*p* ≤ 0.05, *d* = ranging from 1.36 to 2.05) (Figure 2). *Biology* **2021**, *10*, x FOR PEER REVIEW 7 of 11 HIIT group demonstrated a higher training load than those from the HIIT + SSGs group for all weeks (*p* ≤ 0.05, *d* = ranging from 1.36 to 2.05) (Figure 2).

 **Figure 2.** Weekly internal training loads during the 6 weeks combined training interventions. **Figure 2.** Weekly internal training loads during the 6 weeks combined training interventions.

#### **4. Discussion**

**4. Discussion**  The aim of this study was to analyse the effects of exercise order in a combined training programme including SSGs and HIIT. The results of this parallel study revealed no The aim of this study was to analyse the effects of exercise order in a combined training programme including SSGs and HIIT. The results of this parallel study revealed no significant differences between groups (SSGs + HIIT vs. HIIT + SSGs) in the fitness

A combination of SSGs and running-based HIIT was recently tested, aiming to provide the advantageous effect of running-based HIIT to the training programmes based on SSGs [12]. The first reported combination of SSGs and HIIT revealed the beneficial effect of the combination compared to a group using just SSGs for the improvement of VO2max and 30–15 VIFT [15]. However, they did not consider how to implement the combination. Exercise order is of paramount importance. In the first study, testing the effects of exercise order within a training session [20], it was revealed that no significant differences were found between those who completed SSGs + HIIT and those who completed HIIT + SSGs in the 30–15 VIFT [20], which revealed that the internal load imposed was similar between groups. In the present study, the measures of aerobic capacity (i.e., YYIRTL-1 and VO2max) were both meaningfully improved by 6-week training interventions, with no significant difference considering the exercise order. Those findings are not surprising, since both SSGs and running-based HIIT have been repeatedly confirmed as effective in improving aerobic capacity [33,34]. The capacity to sustain high efforts while using both SSGs and running-based HIIT ensures that cardiorespiratory and aerobic systems are taxed by the training stimulus, thus promoting beneficial adaptations [35]. The nonexistence of differences between exercise order is in line with the previous work [20] and sug-

gests that exercise intensity can be independent of the order of implementation.

Considering the effects of combined training intervention on linear sprinting, it was surprising to observe meaningful improvements independent of the exercise order, considering previous reports of combined SSGs + HIIT on such physical quality [14,15]. In fact, the results of the present study showed significant improvements of both groups in

significant differences between groups (SSGs + HIIT vs. HIIT + SSGs) in the fitness

obic capacity, and repeated-sprint ability.

measures collected after the 6-week intervention. However, both combined programmes revealed significant pre–post improvements in linear sprinting, agility, vertical jump, aerobic capacity, and repeated-sprint ability.

A combination of SSGs and running-based HIIT was recently tested, aiming to provide the advantageous effect of running-based HIIT to the training programmes based on SSGs [12]. The first reported combination of SSGs and HIIT revealed the beneficial effect of the combination compared to a group using just SSGs for the improvement of VO2max and 30–15 VIFT [15]. However, they did not consider how to implement the combination.

Exercise order is of paramount importance. In the first study, testing the effects of exercise order within a training session [20], it was revealed that no significant differences were found between those who completed SSGs + HIIT and those who completed HIIT + SSGs in the 30–15 VIFT [20], which revealed that the internal load imposed was similar between groups. In the present study, the measures of aerobic capacity (i.e., YYIRTL-1 and VO2max) were both meaningfully improved by 6-week training interventions, with no significant difference considering the exercise order. Those findings are not surprising, since both SSGs and running-based HIIT have been repeatedly confirmed as effective in improving aerobic capacity [33,34]. The capacity to sustain high efforts while using both SSGs and running-based HIIT ensures that cardiorespiratory and aerobic systems are taxed by the training stimulus, thus promoting beneficial adaptations [35]. The nonexistence of differences between exercise order is in line with the previous work [20] and suggests that exercise intensity can be independent of the order of implementation.

Considering the effects of combined training intervention on linear sprinting, it was surprising to observe meaningful improvements independent of the exercise order, considering previous reports of combined SSGs + HIIT on such physical quality [14,15]. In fact, the results of the present study showed significant improvements of both groups in the 5, 10, 20, and 30 m sprint, thus suggesting the effectiveness of implementing SSGs and HIIT to improve linear sprinting. This fact was not observed in a previous study that combined SSGs and endurance and speed training or in the study that combined SSGs and short-interval (150–150 ) HIIT [15]. In fact, recent systematic reviews with meta-analysis revealed inconsistences and the ineffectiveness of SSGs [12] and HIIT [34] in improving linear sprinting in soccer players. One possible reason for observing improvements in the current research is due to the age effect and the capacity for improvement in this sensitive period [36].

Change of direction (COD) and agility with the ball were both capacities elicited equally by the combination of SSGs + HIIT with no difference considering the exercise order. The use of SSGs and HIIT independently has been suggested as a good way to improve COD [37], while SSGs seem to be better at improving agility with the ball compared to HIIT [38,39]. The combination of both in the present study contributed to meaningfully improving COD and agility with the ball, independent of the exercise order. Again, it seems that exercise order does not affect the capacity of both programmes and training methods to promote beneficial effects in these skills. However, it seems important to highlight the beneficial effect of combining HIIT with regular SSGs, considering a recent meta-analysis that suggested a significant favourable effect of HIIT in comparison to SSGs in improving linear sprint and COD in a within-group analysis [12]. This may be caused by the limited capacity of performing high-intensity linear or curvilinear running activities in small spaces as in the case of SSGs. On the other hand, those small spaces in SSGs can be helpful for promoting greater stimulus in COD and agility with the ball [40].

RSA was also improved after both combined interventions in which exercise order had no significant effect. Recent meta-analysis on the effects of HIIT in soccer revealed a significant favourable effect on RSA [34] in which no significant differences occurred between using HIIT or SSGs [41]. Therefore, due to the specific intermittence and energetic systems associated with both SSGs and HIIT, meaningful improvements in this capacity would be expected [42,43]. Improvements in lower-limb power and sprinting may also be factors benefiting the improvements in RSA [44]. In fact, in the current study, CMJ was also significantly improved in both combined interventions, thus suggesting possible positive effects, despite not being in line with recent meta-analysis about the use of HIIT and SSGs in soccer [12,34] and also compared with a study that combined SSGs + HIIT [45]. It is possible that the age effect and window of improvement may have caused the improvements observed in the current study.

Regarding the consequences of different exercise orders on psychophysiological responses and training load, it was found that HIIT + SSGs had meaningfully lower values of RPE, training load, and enjoyment than the group of SSGs + HIIT. The results regarding the training load are not in line with a previous study that tested the same issue (SSGs vs. HIIT and vice versa), in which no meaningful differences were found [20]. In this case, the psychological effect of more enjoyment while playing SSGs may have affected the perception of load. In fact, consistent results revealed that SSGs induce greater enjoyment than running-based HIIT [1,8,46]. Thus, for the groups ending the session with HIIT, the combination of fatigue and the least enjoyable activity may play an important role in the perceived effort and the enjoyment reported.

This study had some limitations. No control group was implemented; thus, it is not possible to compare the evolution of players without a training intervention or with different training interventions. Additionally, age may be a constraint for the possible generalisation of the findings since the study was conducted in a critical period of evolution. Future studies should compare combined interventions with single training or alternative training methods. Additionally, extending the research to more age groups and normalising the maturation status would be interesting.

#### **5. Conclusions**

The present study showed the order effects of combined SSGs and HIIT on the psychophysiological responses and physical and technical performances of young soccer players. After 6 weeks of combined training interventions, both combined training groups demonstrated similar improvements in physical performance and technical responses. However, the effects of exercise order demonstrated meaningful differences in psychophysiological responses and training load. In terms of practical implications, this study suggests that the combination of SSGs + HIIT is effective in improving the fitness status of adolescent soccer players. However, exercise order does not seem to have a determinant effect on the consequences of the changes in fitness. Therefore, coaches may organise the order based on the most appropriate plans. Future applications should consider implementing strength training in addition to the combination of SSGs + HIIT.

**Author Contributions:** Conceptualisation, E.A., B.K. and Y.S.; methodology, E.A., B.K. and Y.S.; formal analysis, E.A., B.K., F.M.C., Y.S. and M.S.; investigation, E.A., B.K. and M.G.; resources, E.A., B.K., F.M.C., Y.S. and G.B.; data curation, E.A., B.K., F.M.C., Y.S. and M.S.; writing—original draft preparation, E.A., B.K., F.A., F.M.C., Y.S. and M.S.; writing—review and editing, E.A., F.A., F.M.C. and E.M.-C.; visualisation, E.A., B.K. and Y.S.; supervision, E.A., B.K. and Y.S.; project administration, E.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** Filipe Manuel Clemente: This work is funded by Fundação para a Ciência e Tecnologia/Ministério da Ciência, Tecnologia e Ensino Superior through national funds and when applicable co-funded EU funds under the project UIDB/EEA/50008/2020.

**Institutional Review Board Statement:** The study was conducted according to the guidelines ofthe Declaration of Helsinki and approved by the Institutional Ethics Committee of the University of Osmaniye Korkut Ata, Osmaniye, Turkey (Protocol code: 59754796-050.99-E.670, approved on 2 May 2020).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors would like to thank all the players for their efforts.

**Conflicts of Interest:** The authors declare no conflict of interest.
