Jesper Petersen

The preseason Nordic Hamstring Protocol (NHP) reduces hamstring strain injuries in football players. Despite persisting injury rates, elite clubs are reluctant to apply the NHP often over concerns of negative impacts on performance. This pilot study investigated if sprint or jump-performance outcomes tended to increase or decrease following implementation of the NHP in elite male soccer-players. Nineteen male soccer players from the Danish 1st division were randomised to perform NHP (27 sessions) during pre-season, or to control group (CG). Sprint performance (30 m with 5 and 10 m split times) and countermovement jump (CMJ height) was measured before the mid-seasonal break and again after 10 weeks of performing the NHP at the end of pre-season. Dropouts were due to transfers and injuries unrelated to performing NHP (NHP = 0, CG = 5). Sprint performance on the short split distances improved for most players in the NHP (6 out of 9 improved, median changes for 5 m split: − 0.068 s; 10 m split: − 0.078 s), but not CG (2 out of 5 improved, median changes for 5 m split: + 0.1 s; 10 m split: CG: + 0.11 s), but both groups had small declines at 30 m sprint (NHP: 7 out of 9 declined, median changes: + 0.116 s; CG: 4 out of 5 declined, median changes: + 0.159 s). CMJ height mostly improved in both groups (NHP: 6 out of 9 improved, median changes: + 2.1 cm; CG: 4 out of 8 improved, median changes: + 0.55 cm). Performing the NHP in elite soccer players did therefore not seem to negatively affect sprint and vertical jump performance outcomes in the present study, while in fact showing some promise for the more explosive characteristics such as the short 5 and 10 m split-times and maximal CMJ height, which all are highly relevant performance parameters in elite football.

Background: Hamstring injuries are the most common muscle injuries in soccer, and they have a high rate of recurrence. Eccentric hamstrings strength is recognized as an important modifiable risk factor. This led to the development of prevention exercises such as the nordic hamstring exercise (NHE). The effectiveness of the NHE on hamstring injury prevention has never been investigated in amateur soccer. Purpose: To investigate the preventive effect of the NHE on the incidence and severity of hamstring injuries in male amateur soccer players. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: Male amateur soccer players (age, mean ± SD, 24.5 ± 3.8 years) from 40 teams were randomly allocated to an intervention (n = 20 teams, 292 players) or control group (n = 20 teams, 287 players). The intervention group was instructed to perform 25 sessions of NHE in a 13-week period. Both the intervention and control groups performed regular soccer training and were followed for hamstring injury incidence and severity during the 2013 calendar year. At baseline, personal characteristics (eg, age, injury history, field position) were gathered from all participants via a questionnaire. Primary outcome was injury incidence. Secondary outcomes were injury severity and compliance with the intervention protocol. Results: A total of 38 hamstring injuries were recorded, affecting 36 of 579 players (6.2%). The overall injury incidence rate was 0.7 (95% CI, 0.6-0.8) per 1000 player hours, 0.33 (95% CI, 0.25-0.46) in training, and 1.2 (95% CI, 0.82-1.94) in matches. Injury incidence rates were significantly different between the intervention (0.25; 95% CI, 0.19-0.35) and control groups (0.8; 95% CI, 0.61-1.15), χ ² (1, n = 579) = 7.865; P = .005. The risk for hamstring injuries was reduced in the intervention group compared with the control group (odds ratio, 0.282; 95% CI, 0.110-0.721) and was statistically significant ( P = .005). No statistically significant differences were identified between the intervention and control groups regarding injury severity. Compliance with the intervention protocol was 91%. Conclusion: Incorporating the NHE protocol in regular amateur training significantly reduces hamstring injury incidence, but it does not reduce hamstring injury severity. Compliance with the intervention was excellent.

The aim was to investigate performance variables and indicators of cardiovascular health profile in elderly soccer players (SP, n = 11) compared to endurance-trained (ET, n = 8), strength-trained (ST, n = 7) and untrained (UT, n = 7) age-matched men. The 33 men aged 65-85 years underwent a testing protocol including measurements of cycle performance, maximal oxygen uptake (VO2max) and body composition, and muscle fibre types and capillarisation were determined from m. vastus lateralis biopsy. In SP, time to exhaustion was longer (16.3 ± 2.0 min; P < 0.01) than in UT (+48%) and ST (+41%), but similar to ET (+1%). Fat percentage was lower (P < 0.05) in SP (-6.5% points) than UT but not ET and ST. Heart rate reserve was higher (P < 0.05) in SP (104 ± 16 bpm) than UT (+21 bpm) and ST (+24 bpm), but similar to ET (+2 bpm), whereas VO2max was not significantly different in SP (30.2 ± 4.9 ml O2 · min(-1) · kg(-1)) compared to UT (+14%) and ST (+9%), but lower (P < 0.05) than ET (-22%). The number of capillaries per fibre was higher (P < 0.05) in SP than UT (53%) and ST (42%) but similar to ET. SP had less type IIx fibres than UT (-12% points). In conclusion, the exercise performance and cardiovascular health profile are markedly better for lifelong trained SP than for age-matched UT controls. Incremental exercise capacity and muscle aerobic capacity of SP are also superior to lifelong ST athletes and comparable to endurance athletes.

Background Hamstring injuries are the most common muscle injury in male amateur soccer players and have a high rate of recurrence, often despite extensive treatment and long rehabilitation periods. Eccentric strength and flexibility are recognised as important modifiable risk factors, which have led to the development of eccentric hamstring exercises, such as the Nordic hamstring exercise. As the effectiveness of the Nordic hamstring exercise in reducing hamstring injuries has never been investigated in amateur soccer players, the aim of this study is to investigate the effect of this exercise on the incidence and severity of hamstring injuries in male amateur soccer players. An additional aim is to determine whether flexibility is associated with hamstring injuries. Study design Cluster-randomised controlled trial with soccer teams as the unit of cluster. Methods Dutch male amateur soccer players, aged 18–40 years, were allocated to an intervention or control group. Both study groups continued regular soccer training during 2013, but the intervention group additionally performed the Nordic hamstring exercise (25 sessions over 13 weeks). Primary outcomes are the incidence of initial and recurrent hamstring injury and injury severity. Secondary outcomes are hamstring-and-lower-back flexibility and compliance. Compliance to the intervention protocol was also monitored. Discussion Eccentric hamstring strength exercises are hypothesised to reduce the incidence of hamstring injury among male amateur soccer players by 70%. The prevention of such injuries will be beneficial to soccer players, clubs, football associations, health insurance companies and society. Trial Registration NTR3664.

Background: An injury to the hamstring muscle complex is the most common injury in soccer. Ultrasound of acute hamstring injuries is often used as a clinical tool for diagnosing hamstring injuries and guiding players in when they can return to play. Purpose: To (1) investigate the characteristic sonographic findings of acute hamstring injuries in soccer players, (2) compare the mean injury severity (time to return to play) in injured players with and without sonographically verified abnormalities, and (3) correlate the length of the injured area and absence from soccer play (time to return to play) to investigate if ultrasonography can be used as a prognostic indicator of time to return to play. Study Design: Case series; Level of evidence, 4. Methods: Players from 50 teams participating in 1 of the top 5 Danish soccer divisions were followed in the period from January to December 2008. Of 67 players with acute hamstring injuries, 51 underwent ultrasonographic examination of the injured thigh and were included in this study. Results: Ultrasonographic examinations were performed 1 to 10 days after injury (mean, 5.2 ± 3.0 days), and sonographic findings were present in 31 of 51 cases (61%). Two thirds of the injuries were to the biceps femoris muscle and one third to the semitendinosus muscle. No total ruptures were documented. The 51 acute hamstring injuries resulted in absence from soccer of a mean 25.4 ± 15.7 days per injury, with no significant difference between players with and without sonographically verified abnormalities (P = .41). No correlation existed between the length of the injured area and injury severity (r = 0.19, P = .29). Conclusion: The biceps femoris is the most commonly injured hamstring muscle detected by ultrasound, and more than half of the injuries are intramuscular. Because neither the presence of sonographic findings nor the size of the findings was correlated with time to return to play in injured soccer players, the prognosis of hamstring injuries should not be guided by these findings alone.

Non-operative treatment of acute hip adductor longus ruptures in athletes has been described in the literature. However, very limited information concerning the recovery of this type of injury exists. This case represented a unique possibility to study the recovery of two acute adductor longus ruptures, using novel, reliable and validated assessment methods.

This study examined the effect of 12 weeks of small-sided street soccer (2.2 ± 0.7 sessions/week) and fitness center training (0.5 ± 0.2 sessions/week) on physical fitness and cardiovascular health profile for homeless men. Exercise capacity, maximal oxygen uptake (VO_2max), body composition (DXA scans), blood pressure (BP), and blood lipid profile were determined before and after the intervention period for 22 soccer-group subjects (SG) and 10 waiting list controls (CO). In addition, time-motion analyses, HR measurements, and pedometer recordings were performed during street soccer training and daily-life activities. During a 60 min 4 versus 4 street soccer session 182 ± 62 intense running bouts were performed; mean HR was 82 ± 4% HR_max and HR was >90% HR_max for 21 ± 12% (±SD) of total time. On a day without training the participants performed 10,733 ± 4,341 steps and HR was >80% HR_max for 2.4 ± 4.3 min. In SG, VO_2max was elevated (p < 0.05) from 36.7 ± 7.6 to 40.6 ± 8.6 ml/min/kg after 12 weeks and incremental cycle test performance was improved (p < 0.05) by 81 s (95% CI: 47–128 s). After 12 weeks, fat percentage (19.4 ± 8.5 to 17.5 ± 8.6%) and LDL cholesterol (3.2 ± 1.1 to 2.8 ± 0.8 mmol L⁻¹) were lowered (p < 0.05) in SG. The observed changes in SG were different (p < 0.05) from CO and no intra-group changes occurred for CO (p > 0.05). BP was unaltered after 12 weeks (p > 0.05), but diastolic BP was lowered for all SG subjects with pre-values >75 mmHg (83 ± 6 to 76 ± 6 mmHg, n = 8, p < 0.05). In conclusion, the exercise intensity is high during street soccer and regular street soccer training can be used as an effective activity to promote physical fitness and cardiovascular health status for homeless men.

Background: The incidence of acute hamstring injuries is high in several sports, including the different forms of football. Purpose: The authors investigated the preventive effect of eccentric strengthening of the hamstring muscles using the Nordic hamstring exercise compared with no additional hamstring exercise on the rate of acute hamstring injuries in male soccer players. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: Fifty Danish male professional and amateur soccer teams (942 players) were allocated to an intervention group (461 players) or a control group (481 players). Players in the intervention group conducted a 10-week progressive eccentric training program followed by a weekly seasonal program, whereas players in the control group followed their usual training program. The main outcome measures were numbers of overall, new, and recurrent acute hamstring injuries during 1 full soccer season. Results: Fifty-two acute hamstring injuries in the control group compared with 15 injuries in the intervention group were registered. Comparing intervention versus the control group, overall acute hamstring injury rates per 100 player seasons were 3.8 versus 13.1 (adjusted rate ratio [RR], 0.293; 95% confidence interval [CI], 0.150-0.572; P < .001). New injury rates per 100 player seasons were 3.1 versus 8.1 (RR, 0.410; 95% CI, 0.180-0.933; P = .034), whereas recurrent injury rates per 100 player seasons were 7.1 versus 45.8 (RR, 0.137; 95% CI, 0.037-0.509; P = .003). Number needed to treat [NNT] to prevent 1 acute hamstring injury (new or recurrent) is 13 (95% CI, 9-23) players. The NNT to prevent 1 new injury is 25 (95% CI, 15-72) players, and NNT to prevent 1 recurrent injury is 3 (95% CI, 2-6) players. Conclusion: In male professional and amateur soccer players, additional eccentric hamstring exercise decreased the rate of overall, new, and recurrent acute hamstring injuries.

Background Valid, reliable and responsive Patient-Reported Outcome (PRO) questionnaires for young to middle-aged, physically active individuals with hip and groin pain are lacking. Objective To develop and validate a new PRO in accordance with the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) recommendations for use in young to middle-aged, physically active patients with long-standing hip and/or groin pain. Methods Preliminary patient interviews (content validity) included 25 patients. Validity, reliability and responsiveness were evaluated in a clinical study including 101 physically active patients (50 women); mean age 36 years, range 18–63 years. Results The Copenhagen Hip and Groin Outcome Score (HAGOS) consists of six separate subscales assessing Pain, Symptoms, Physical function in daily living, Physical function in Sport and Recreation, Participation in Physical Activities and hip and/or groin-related Quality of Life (QOL). Test–retest reliability was substantial, with intraclass correlation coefficients ranging from 0.82 to 0.91 for the six subscales. The smallest detectable change ranged from 17.7 to 33.8 points at the individual level and from 2.7 to 5.2 points at the group level for the different subscales. Construct validity and responsiveness were confirmed with statistically significant correlation coefficients (0.37–0.73, p < 0.01) for convergent construct validity and for responsiveness from 0.56 to 0.69, p < 0.01. Conclusion HAGOS has adequate measurement qualities for the assessment of symptoms, activity limitations, participation restrictions and QOL in physically active, young to middle-aged patients with long-standing hip and/or groin pain and is recommended for use in interventions where the patient's perspective and health-related QOL are of primary interest. Trial registration ClinicalTrials.gov NCT00716729