Small-sided games (SSG) are played on a small pitch, often using modified rules and involving a smaller number of players. This article aimed to critically analyse the literature to determine how small-sided games affect the performance of football players in the short- and long term. Electronic databases were searched for literature dating from January 2000 to July 2018. The methodological quality of the studies was evaluated using the modified Downs and Black Quality Index (cross-sectional studies) and the Physiotherapy Evidence Database (PEDro) scale (intervention studies). Fifty-three studies, 44 cross-sectional and 9 intervention studies, met the inclusionary criteria for review. Most of the cross-sectional studies focused on describing the differences between SSG protocols, whereas 4 studies focused on making a comparison between "interval" and "continuous" SSG training regimes. On the other hand, intervention studies focused on making a comparison between SSG-based protocols and high-intensity intermittent training (HIIT)-based running protocols, in addition to determine the effect of a SSG-based training programme alone. SSG-based football plans (2 to 4 SSG sessions per week) show athletic performance improvements in football players by improving sprint, repeated sprint ability (RSA) and change of direction (COD) along with muscular and physiological adaptation.

Ramirez-Campillo, R, Alvarez, C, García-Pinillos, F, Sanchez-Sanchez, J, Yanci, J, Castillo, D, Loturco, I, Chaabene, H, Moran, J, and Izquierdo, M. Optimal reactive strength index: is it an accurate variable to optimize plyometric training effects on measures of physical fitness in young soccer players? J Strength Cond Res 32(4): 885–893, 2018—This study aimed to compare the effects of drop-jump training using a fixed drop-box height (i.e., 30-cm [FIXED]) vs. an optimal (OPT) drop-box height (i.e., 10-cm to 40-cm: generating an OPT reactive strength index [RSI]) in youth soccer players' physical fitness. Athletes were randomly allocated to a control group (n = 24; age = 13.7 years), a fixed drop-box height group (FIXED, n = 25; age = 13.9 years), or an OPT drop-box height group (OPT, n = 24; age = 13.1 years). Before and after 7 weeks of training, tests for the assessment of jumping (countermovement jump [CMJ], 5 multiple bounds), speed (20-m sprint time), change of direction ability (CODA [Illinois test]), strength {RSI and 5 maximal squat repetition test (5 repetition maximum [RM])}, endurance (2.4-km time trial), and kicking ability (maximal kicking distance) were undertaken. Analyses revealed main effects of time for all dependent variables (p < 0.001, d = 0.24–0.72), except for 20-m sprint time. Analyses also revealed group × time interactions for CMJ (p < 0.001, d = 0.51), depth jump (DJ) (p < 0.001, d = 0.30), 20-m sprint time (p < 0.001, d = 0.25), CODA (p < 0.001, d = 0.22), and 5RM (p < 0.01, d = 0.16). Post hoc analyses revealed increases for the FIXED group (CMJ: 7.4%, d = 0.36; DJ: 19.2%, d = 0.49; CODA: −3.1%, d = −0.21; 5RM: 10.5%, d = 0.32) and the OPT group (CMJ: 16.7%, d = 0.76; DJ: 36.1%, d = 0.79; CODA: −4.4%, d = −0.34; 5RM: 18.1%, d = 0.47). Post hoc analyses also revealed increases for the OPT group in 20-m sprint time (−3.7%, d = 0.27). Therefore, to maximize the effects of plyometric training, an OPT approach is recommended. However, using adequate fixed drop-box heights may provide a rational and practical alternative.

The purpose of this study was to determine the effects of a 12-week contrast training (CT) program (isometric + plyometric), with no external loads, on the vertical jump, kicking speed, sprinting, and agility skills of young soccer players. Thirty young soccer players (age, 15.9 ± 1.43 years; weight, 65.4 ± 10.84 kg; height, 171.0 ± 0.06 cm) were randomized in a control group (n = 13) and an experimental group (n = 17). The CT program was included in the experimental group's training sessions, who undertook it twice a week as a part of their usual weekly training regime. This program included 3 exercises: 1 isometric and 2 plyometric, without external loads. These exercises progressed in volume throughout the training program. Performance in countermovement jump (CMJ), Balsom agility test (BAT), 5-, 10-, 20-, and 30-m sprint, and soccer kick were assessed before and after the training program. A 2-factor (group and time) analysis of variance revealed significant improvements (p < 0.001) in CMJ, BAT, and kicking speed in the experimental group players. Control group remained unchanged in these variables. Both groups significantly reduced sprint times over 5, 10, 20, and 30 m (p ≤ 0.05). A significant correlation (r = 0.492, p < 0.001) was revealed between ΔBAT and Δaverage kicking speed. Results suggest that a specific CT program without external loads is effective for improving soccer-specific skills such as vertical jump, sprint, agility, and kicking speed in young soccer players.

This study aims to analyse the impact of limited hamstring flexibility (HF) on specific football skills, such as sprinting and jumping ability, agility, and kicking speed in young football players. Forty-three male football players (aged 14-18) from a semi-professional football academy participated voluntarily in this study. Data about anthropometric measurements, HF (unilateral passive straight-leg raise test: PSLR), vertical jumping ability (countermovement jump: CMJ), sprinting ability (5, 10, 20 m: S5 m, S10 m, S20 m), agility (Balsom agility test: BAT), and kicking speed in terms of ball speed (dominant and non-dominant leg: KSdom and KSnon-dom) were collected. Cluster analysis grouped according to HF, dividing participants into a flexible group (FG, n = 24) and a non-flexible group (NFG, n = 19) in relation to performances on the PSLR test. Despite finding no significant differences between groups in body composition and age, the FG performed better in terms of sprint scores (S5 m: 6.12%, S10 m: 4.09%, S20 m: 3.29%), BAT score (4.11%), CMJ score (10.49%), and scores for KSdom (6.86%) and KSnon-dom (8%) than the NFG. The results suggest that HF is a key factor for performing football-specific skills, such as sprinting, jumping, agility, and kicking in young football players. These results support the rationale that muscle flexibility must be specifically trained in football players beginning at early ages.

Plyometric jump training (PJT) is a frequently used and effective means to improve amateur and elite soccer players' physical fitness. However, it is unresolved how different PJT frequencies per week with equal overall training volume may affect training-induced adaptations. Therefore, the aim of this study was to compare the effects of an in-season 8 week PJT with one session vs. two sessions per week and equal training volume on components of physical fitness in amateur female soccer players. A single-blind randomized controlled trial was conducted. Participants (N = 23; age, 21.4 ± 3.2 years) were randomly assigned to a one session PJT per-week (PJT-1, n = 8), two sessions PJT per-week (PJT-2, n = 8) or an active control group (CON, n = 7). Before and after training, participants performed countermovement jumps (CMJ), drop-jumps from a 20-cm drop-height (DJ20), a maximal kicking velocity test (MKV), the 15-m linear sprint-time test, the Meylan test for the assessment of change of direction ability (CoDA), and the Yo-Yo intermittent recovery endurance test (Yo-YoIR1). Results revealed significant main effects of time for the CMJ, DJ20, MKV, 15-m sprint, CoDA, and the Yo-YoIR1 (all p < 0.001; d = 0.57–0.83). Significant group × time interactions were observed for the CMJ, DJ20, MKV, 15-m sprint, CoDA, and the Yo-YoIR1 (all p < 0.05; d = 0.36–0.51). Post-hoc analyses showed similar improvements for PJT-1 and PJT-2 groups in CMJ (Δ10.6%, d = 0.37; and Δ10.1%, d = 0.51, respectively), DJ20 (Δ12.9%, d = 0.47; and Δ13.1%, d = 0.54, respectively), MKV (Δ8.6%, d = 0.52; and Δ9.1%, d = 0.47, respectively), 15-m sprint (Δ8.3%, d = 2.25; and Δ9.5%, d = 2.67, respectively), CoDA (Δ7.5%, d = 1.68; and Δ7.4%, d = 1.16, respectively), and YoYoIR1 (Δ10.3%, d = 0.22; and Δ9.9%, d = 0.26, respectively). No significant pre-post changes were found for CON (all p > 0.05; Δ0.5–4.2%, d = 0.03–0.2). In conclusion, higher PJT exposure in terms of session frequency has no extra effects on female soccer players' physical fitness development when jump volume is equated during a short-term (i.e., 8 weeks) training program. From this, it follows that one PJT session per week combined with regular soccer-specific training appears to be sufficient to induce physical fitness improvements in amateur female soccer players.

High-intensity interval training (HIIT) can produce similar or improved results compare with traditional training, but the question as to whether HIIT can be used in the setting of physical education (PE) remains unanswered. The aim of this systematic review was to critically analyze the feasibility of incorporating HIIT programs into PE classes to improve the body compositions and cardiorespiratory fitness of overweight students. We conducted database searches for literature dating between January 2012 and January 2017. Of the final six studies selected, three were conducted in children under 12 years old and three involved adolescents between 12 and 18 years old. The HIIT protocols consisted of 2-3 sessions per week, with intervals of 15 s and passive or active rests of 15 s, totaling up to 6 min of work with 4 min of rest. The duration of HIIT programs was 6-24 weeks. Significant changes were reported in body composition, body mass index, body fat (%), waist circumference, and sum of skinfolds; and increases in muscle mass were observed. The inclusion of HIIT programmes improved maximal oxygen uptake (VO2max), performance in the intermittent Yo-Yo test and maximal aerobic speed. The HIIT programmes showed improvements in the variables studied, with interventions two or three times weekly. Therefore, they can be used in schools, as a strategy to combat the childhood obesity pandemic and HIIT can be use alongside with existing PE activities within the same lesson or in specific periods during day school.