Background Given the severe economic and performance implications of hamstring injuries, there are different attempts to identify their risk factors for subsequently developing injury prevention strategies to reduce the risk of these injuries. One of the strategies reported in the scientific literature is the application of interventions with eccentric exercises. To verify the effectiveness of these interventions, different eccentric strength measurements have been used with low-cost devices as alternatives to the widespread used isokinetic dynamometers and the technically limited handheld dynamometers. Therefore, the purpose of the present systematic review was to summarize the findings of the scientific literature related to the evaluation of eccentric strength of hamstring muscles with these new technologies. Methods Systematic searches through the PubMed, Scopus, and Web of Science databases, from inception up to April 2020, were conducted for peer reviewed articles written in English, reporting eccentric strength of hamstrings assessed by devices, different to isokinetic and handheld dynamometers, in athletes. Results Seventeen studies were finally included in the review with 4 different devices used and 18 parameters identified. The pooled sample consisted of 2893 participants (97% male and 3% female: 22 ± 4 years). The parameters most used were peak force (highest and average), peak torque (average and highest), and between-limb imbalance (left-to-right limb ratio). There is inconsistency regarding the association between eccentric hamstrings strength and both injury risk and athletic performance. There is no standardized definition or standardization of the calculation of the used parameters. Conclusions The current evidence is insufficient to recommend a practical guide for sports professionals to use these new technologies in their daily routine, due to the need for standardized definitions and calculations. Furthermore, more studies with female athletes are warranted. Despite these limitations, the eccentric strength of hamstring muscles assessed by different devices may be recommended for monitoring the neuromuscular status of athletes.

Purpose. the study analysed the responses from different training load monitoring tools in the elite U-20 soccer category and checked the level of association between these responses. Methods. the participants were 10 elite male soccer players (age, 18.61 ± 0.95 years; height, 176.81 ± 5.03 cm; body mass, 70.32 ± 8.41 kg). the progressive test to exhaustion assessed maximum oxygen consumption and maximum heart rate. the athletes were monitored over 15 training sessions with a heart-rate-based method (Edwards) and mechanical load indicators obtained from GPS devices (15 Hz). Results. Individual training load was calculated with the Foster's session rating of perceived exertion (session-rPE) procedure. A significant correlation was found between session-rPE and Edwards (0.564, p < 0.05). there were no significant correlations between session-rPE and average speed (-0.161), average heart rate of the training session (-0.187), distance over 20 km/h (0.006), or number of accelerations performed in different zones (-0.194,-0.178,-0.171,-0.236). the Edwards method showed significant correlations with the total distance (0.642, p < 0.01), average heart rate (0.333, p < 0.01), and distances covered at 0-20 km/h (0.634, p < 0.01; 0.568, p < 0.01; 0.424, p < 0.01; 0.289, p < 0.01; 0.201, p < 0.015). there were no significant correlations between Edwards and average speed (0.158), distance over 20 km/h (0.014), number of accelerations performed in different zones (-0.194,-0.178,-0.171,-0.236), or number of normalized accelerations (-0.118,-0.038,-0.058,-0.035). Conclusions. the Edwards method and session-rPE are limited load monitoring tools to indicate the reality of training situations (high-intensity action with recovery intervals).

This study investigated the differences in external and internal load during pre-season training sessions carried out with different SSGs and a friendly match in top-class professional football players. The study was conducted over a full pre-season. Participants were 9 male top-class professional football players (25 ± 5 years; 74 ± 8 kg; 177 ± 8 cm). The following variables were measured: training session duration (min), average heart rate (bpm), total distance (m), distance covered per minute (m/min), the total number of accelerations > 2.5 m/s2, number of accelerations > 2.5 m/s2 per minute, average distance of accelerations (m), the average value of acceleration (m/s2). One-way ANOVA was performed to analyze the variance of all evaluated variables. No differences were found in the average accelerations (m/s2) (0.128) among all the training formats. Moderate differences were found in number of accelerations > 2.5 m/s2 per minute (η2 = 0.396, moderate effect) and average distance of accelerations (η2 = 0.545). Strong differences were found in HR (η2 = 0.788, large effect), total distance (η2 = 0.797, strong effect), distance per minute (η2 = 0.775 strong effect), total number of accelerations > 2.5 m/s2 (η2 = 0.699 strong effect). Significant correlations were found just for the number of accelerations > 2.5 m/s2 and the number of accelerations > 2.5 m/s2 per minute with the 4v4, 8v8 and the FM (r = 0.828–0.890, r2 = 69% – 79%; p < 0.01). External and internal loads differ across different SSGs and a FM during the pre-season training sessions.