Background: Eccentric resistance training is recognised as an effective stimulus for enhancing measures of muscular strength and power in adult populations; however, its value in youth athletes is currently not well understood. Objective: The aim of this systematic review was to critically appraise the effects of eccentric resistance training on measures of physical performance (i.e. muscular strength, jump, sprint and change of direction) in youth athletes 18 years of age and under. Methods: Original journal articles published between 1950 and June 2022 were retrieved from electronic search engines of PubMed, SPORTDiscus and Google Scholar’s advanced search option. Full journal articles investigating the acute and chronic effects of eccentric resistance training on measures of physical performance in youth athletes (i.e. a person 18 years of age or under who competes in sport) were included. The methodological quality and bias of each study were assessed prior to data extraction using a modified Downs and Black checklist. Results: The search yielded 749 studies, of which 436 were duplicates. Three-hundred studies were excluded based upon title and abstract review and a further 5 studies were removed following the modified Downs and Black checklist. An additional 14 studies were identified during backward screening. Accordingly, 22 studies were included in our systematic review. The Nordic hamstring exercise and flywheel inertial training were the most frequently used eccentric resistance training methods in youth athletes. Improvements in physical performance following the Nordic hamstring exercise are dependent upon an increase in the breakpoint angle, rather than training volume (sets and repetitions), and are further elevated with the addition of hip extension exercises or high-speed running. A minimum of 3 familiarisation trials is necessary to elicit meaningful adaptations following flywheel inertial training. Furthermore, an emphasis should be placed upon decelerating the rotating flywheel during the final one to two thirds of the eccentric phase, rather than gradually throughout the entire eccentric phase. Conclusions: The findings of this systematic review support the inclusion of eccentric resistance training in youth athletes to improve measures of muscular strength, jump, sprint and change of direction performance. The current eccentric resistance training methods are predominantly limited to the Nordic hamstring exercise and flywheel inertial training; however, the efficacy of accentuated eccentric loading to improve jump performance warrants attention in future investigations.

Jeffreys, MA, De Ste Croix, MBA, Lloyd, RS, Oliver, JL, and Hughes, JD. The effect of varying plyometric volume on stretch-shortening cycle capability in collegiate male rugby players. J Strength Cond Res 33(1): 139–145, 2019—The purpose of this study was to identify the effectiveness of low and high volume plyometric loads on developing stretch-shortening cycle capability in collegiate rugby players. A between-group repeated measures design was used. Thirty-six subjects (age 20.3 ± 1.6 years, mass 91.63 ± 10.36 kg, stature 182.03 ± 5.24 cm) were randomly assigned to one of 3 groups: a control group (CG), a low volume plyometric group (LPG), or a high volume plyometric group (HPG). Data were collected from a force plate, and measures of reactive strength index (RSI) and leg stiffness were calculated from jump height, contact time, and flight time. A significant between-group × time (F = 4.01, p ≤ 0.05) interaction effect for RSI was observed. Bonferroni post hoc analysis indicated that both the LPG training group (p = 0.002) and HPG training group (p = 0.009) were significantly higher than the control group. No significant interaction effect between time × group was observed for leg stiffness (F = 1.39, p = 0.25). This study has demonstrated that it is possible to improve reactive strength capabilities through the use of a low volume plyometric program. The low volume program elicited the same performance improvement in RSI as a high volume program while undertaking a lower dose. This suggests that strength and conditioning coaches may be able to benefit from the ability to develop more time-efficient and effective plyometric programs.

Hughes, JD, Massiah, RG, and Clarke, RD. The potentiating effect of an accentuated eccentric load on countermovement jump performance. J Strength Cond Res 30(12): 3450–3455, 2016—Postactivation potentiation (PAP) following a bout of high-intensity exercise of short duration is known to produce both a fatigued and a potentiated state. There has been much research in the effectiveness of various PAP protocols, yet the type of dynamic muscle action utilized has seldom been investigated. Therefore, the present study aimed to assess whether an accentuated eccentric load (AE) could enhance subsequent performance. Eleven men (21 ± 2 years, 179.1 ± 6.9 cm, 83.2 ± 10.1 kg) performed 3 countermovement jumps (CMJs) before and 6 minutes after an AE and a back squat (BSq) PAP protocol. The participant's maximum CMJ height (cm) was determined before and after both protocol. A 2-way repeated measures analysis of variance was conducted to evaluate the effect of PAP condition and time on vertical jumping performance. A significant condition × time interaction was found (p = 0.02). Post hoc tests revealed that AE PAP had a significant (p = 0.03) potentiating effect on CMJ jump height. Whereas, the BSq PAP revealed no significant differences (p = 0.32). In conclusion, this study has shown that jump performance can be enhanced by eccentric muscle action when compared with a traditional BSq PAP protocol. This may provide a more practical method for coaches to enhance short-term explosive movements in athletic populations.

Background: It has been suggested that altering the knee flexion angle during a commonly used supine isometric strength test developed with professional soccer players changes preferential hamstring muscle recruitment. The aim of this study was to examine the electromyography (EMG) knee joint-angle relationship during this test, as these data are currently unknown. Methods: Ten recreational male soccer athletes (age: 28 ± 2.4 years) were recruited and performed a supine isometric strength test on their dominant leg with the knee placed at two pre-selected flexion angles (30° and 90°). The surface EMG of the gluteus maximus, biceps femoris, semitendinosus, and medial gastrocnemius was measured, in addition to the within-session reliability (intraclass correlation coefficient (ICC) and coefficient of variation (CV)). Results: Within-session reliability showed large variation dependent upon the test position and muscle measured (CV% = 8.8–36.1) Absolute mean EMG activity and percentage of maximum voluntary isometric contraction (MVIC) indicated different magnitudes of activation between the two test positions; however, significant mean differences were present for the biceps femoris only with greater activation recorded at the 30° knee angle (% MVIC: 31 ± 9 vs. 22 ± 7; p = 0.002). These differences (30% mean difference) were greater than the observed typical measurement error (CV% = 13.1–14.3 for the 90° and 30° test positions, respectively). Furthermore, the percentage MVIC showed a trend of heightened activation of all muscles with the knee positioned at 30°, but there was also more within-subject variation, and this was more pronounced for the gluteus maximus (CV% = 36.1 vs. 19.8) and medial gastrocnemius (CV% 31 vs. 22.6). Conclusions: These results indicate that biceps femoris and overall posterior chain muscle activation is increased with the knee positioned at 30° of flexion; however, the 90° angle displayed less variation in performance within individual participants, especially in the gluteus maximus and medial gastrocnemius. Thus, practitioners using this test to assess hamstring muscle strength should ensure appropriate familiarisation is afforded, and then may wish to prioritise the 30° knee position.