Mette K. Zebis

Muscle Activation and Perceived Loading During Rehabilitation Exercises: Comparison of Dumbbells and Elastic Resistance

Background High-intensity resistance training plays an essential role in the prevention and rehabilitation of musculoskeletal injuries and disorders. Although resistance exercises with heavy weights yield high levels of muscle activation, the efficacy of more user-friendly forms of exercise needs to be examined. Objective The aim of this study was to investigate muscle activation and perceived loading during upper-extremity resistance exercises with dumbbells compared with elastic tubing. Design A single-group, repeated-measures study design was used. Setting Exercise evaluation was conducted in a laboratory setting. Participants Sixteen female workers (aged 26–55 years) without serious musculoskeletal diseases and with a mean neck and shoulder pain intensity of 7.8 on a 100-mm visual analog scale participated in the study. Measurements Electromyographic (EMG) activity was measured in 5 selected muscles during the exercises of lateral raise, wrist extension, and shoulder external rotation during graded loadings with dumbbells (2–7.5 kg) and elastic tubing (Thera-Band, red to silver resistance). The order of exercises and loadings was randomized for each individual. Electromyographic amplitude was normalized to the absolute maximum EMG amplitude obtained during maximal voluntary isometric contraction and exercise testing. Immediately after each set of exercise, the Borg CR10 scale was used to rate perceived loading during the exercise. Results Resistance exercise with dumbbells as well as elastic tubing showed increasing EMG amplitude and perceived loading with increasing resistance. At the individually maximal level of resistance for each exercise—defined as the 3 repetitions maximum—normalized EMG activity of the prime muscles was not significantly different between dumbbells (59%–87%) and elastic tubing (64%–86%). Perceived loading was moderately to very strongly related to normalized EMG activity (r=.59–.92). Limitations The results of this study apply only for exercises performed in a controlled manner (ie, without sudden jerks or high acceleration). Conclusions Comparably high levels of muscle activation were obtained during resistance exercises with dumbbells and elastic tubing, indicating that therapists can choose either type in clinical practice. The Borg CR10 can be a useful aid in estimating intensity of individual rehabilitation protocols.

Identification of Athletes at Future Risk of Anterior Cruciate Ligament Ruptures by Neuromuscular Screening

Background A high percentage of female athletes who sustain an anterior cruciate ligament (ACL) rupture suffer serious long-term consequences such as osteoarthritis and disability. Thus, identification of risk factors has high clinical relevance in the prevention of ACL rupture. Hypothesis Noninjured athletes with low knee flexor electromyography (EMG) preactivity and high knee extensor EMG preactivity during sidecutting are at increased risk of future ACL rupture. Study Design Cohort study (prognosis); Level of evidence, 2. Methods Fifty-five elite female athletes (team handball and soccer) aged 24 ± 5 years with no history of ACL injury were tested for EMG preactivity of vastus lateralis and medialis, rectus femoris, semitendinosus, and biceps femoris during a standardized side-cutting maneuver. The incidence of ACL ruptures was registered in the following 2 match seasons. Results During the subsequent 2 match seasons, 5 athletes sustained a confirmed noncontact ACL rupture. Before injury, all 5 players displayed a neuromuscular pattern that differed from the noninjured players, characterized by reduced EMG preactivity for the semitendinosus (ST) and elevated EMG preactivity for the vastus lateralis (VL) (P < .01). On the basis of these findings, a high-risk zone was defined as one standard deviation above the mean VL-ST difference. In our population, 5 of 10 subjects with a VL-ST difference in this zone sustained an ACL injury during the study period. Conclusion In the present study, currently noninjured female athletes with reduced EMG preactivity of the ST and increased EMG preactivity of the VL during side cutting were at increased risk of future noncontact ACL rupture. Our data indicate that a high-risk zone can be used to identify noninjured players at high risk of future ACL rupture. Consequently, individual preventive efforts can be introduced in time. However, large prospective studies are needed to confirm this finding before definitive clinical recommendations can be made.

The effects of neuromuscular training on knee joint motor control during sidecutting in female elite soccer and handball players.

Objective:The project aimed to implement neuromuscular training during a full soccer and handball league season and to experimentally analyze the neuromuscular adaptation mechanisms elicited by this training during a standardized sidecutting maneuver known to be associated with non-contact anterior cruciate ligament (ACL) injury. Design:The players were tested before and after 1 season without implementation of the prophylactic training and subsequently before and after a full season with the implementation of prophylactic training. Participants:A total of 12 female elite soccer players and 8 female elite team handball players aged 26 ± 3 years at the start of the study. Intervention:The subjects participated in a specific neuromuscular training program previously shown to reduce non-contact ACL injury. Methods:Neuromuscular activity at the knee joint, joint angles at the hip and knee, and ground reaction forces were recorded during a sidecutting maneuver. Neuromuscular activity in the prelanding phase was obtained 10 and 50 ms before foot strike on a force plate and at 10 and 50 ms after foot strike on a force plate. Results:Neuromuscular training markedly increased before activity and landing activity electromyography (EMG) of the semitendinosus (P < 0.05), while quadriceps EMG activity remained unchanged. Conclusions:Neuromuscular training increased EMG activity for the medial hamstring muscles, thereby decreasing the risk of dynamic valgus. This observed neuromuscular adaptation during sidecutting could potentially reduce the risk for non-contact ACL injury.

Effectiveness of small daily amounts of progressive resistance training for frequent neck/shoulder pain: Randomised controlled trial

&NA; Regular physical exercise is a cornerstone in rehabilitation programs, but adherence to comprehensive exercise remains low. This study determined the effectiveness of small daily amounts of progressive resistance training for relieving neck/shoulder pain in healthy adults with frequent symptoms; 174 women and 24 men working at least 30 h per week and with frequent neck/shoulder pain were randomly assigned to resistance training with elastic tubing for 2 or 12 minutes per day 5 times per week, or weekly information on general health (control group). Primary outcomes were changes in intensity of neck/shoulder pain (scale 0 to 10), examiner‐verified tenderness of the neck/shoulder muscles (total tenderness score of 0 to 32), and isometric muscle strength at 10 weeks. Compared with the control group, neck/shoulder pain and tenderness, respectively, decreased 1.4 points (95% confidence interval −2.0 to −0.7, p < 0.0001) and 4.2 points (95% confidence interval −5.7 to −2.7, p < 0.0001) in the 2‐minute group and 1.9 points (95% confidence interval −2.5 to −1.2, p < 0.0001) and 4.4 points (95% confidence interval −5.9 to −2.9, p < 0.0001) in the 12‐minute group. Compared with the control group, muscle strength increased 2.0 Nm (95% confidence interval 0.5 to 3.5 Nm, p = 0.01) in the 2‐minute group and 1.7 Nm (95% confidence interval 0.2 to 3.3 Nm, p = 0.02) in the 12‐minute group. In conclusion, as little as 2 minutes of daily progressive resistance training for 10 weeks results in clinically relevant reductions of pain and tenderness in healthy adults with frequent neck/shoulder symptoms. Trial registration: www.isrctn.org/ISRCTN60264809. In generally healthy adults with frequent neck/shoulder muscle pain, as little as 2 minutes of daily progressive resistance training reduces pain and tenderness.

Game-induced fatigue patterns in elite female soccer.

Krustrup, P, Zebis, M, Jensen, JM, and Mohr, M. Game-induced fatigue patterns in elite female soccer. J Strength Cond Res 24(2): 437-441, 2010-The purpose was to examine the fatigue pattern of elite female soccer players after competitive games. Soccer players (n = 23) from the Danish women Premier League performed a countermovement vertical jump test, a repeated 30-m sprint test, and the Yo-Yo intermittent endurance level 2 (Yo-Yo IE2) test at rested state and after a competitive game. Average heart rate during the game was 86 ± 1% of maximal heart rate with no differences between halves. Blood lactate was 5.1 ± 0.5 mmol·L−1 after the first half, which was higher (p < 0.05) than after the second half (2.7 ± 0.4 mmol·L−1). Yo-Yo IE2 performance was 484 ± 50 m after the game, which was 62% lower (p < 0.05) than at rested state (1,265 ± 133 m). Average sprinting time of three 30-m sprints was 5.06 ± 0.06 seconds after the game, which was 4% slower (p < 0.05) than at rest (4.86 ± 0.06 seconds). No game-induced effect was observed on vertical jump performance. Significant inverse correlations were observed between Yo-Yo IE2 test performance and fatigue index during the repeated sprint test both at rest (r = −0.76, p < 0.05) and after the game (r = −0.66, p < 0.05). The study demonstrates that the type of fatigue that occurs after a female soccer game does cause marked impairment in intense intermittent exercise and repeated sprint performance but does not affect vertical jump performance. These findings support the notion that decrements in distance covered by sprinting and high-speed running toward the end of elite female games are caused by fatigue.

Implementation of neck/shoulder exercises for pain relief among industrial workers: a randomized controlled trial.

BackgroundAlthough leisure-time physical activity is important for health, adherence to regular exercise is challenging for many adults. The workplace may provide an optimal setting to reach a large proportion of the adult population needing regular physical exercise. This study evaluates the effect of implementing strength training at the workplace on non-specific neck and shoulder pain among industrial workers.MethodsCluster-randomized controlled trial involving 537 adults from occupations with high prevalence of neck and shoulder pain (industrial production units). Participants were randomized to 20 weeks of high-intensity strength training for the neck and shoulders three times a week (n = 282) or a control group receiving advice to stay physically active (n = 255). The strength training program followed principles of progressive overload and periodization. The primary outcome was changes in self-reported neck and shoulder pain intensity (scale 0-9).Results85% of the participants followed the strength training program on a weekly basis. In the training group compared with the control group, neck pain intensity decreased significantly (-0.6, 95% CI -1.0 to -0.1) and shoulder pain intensity tended to decrease (-0.2, 95% CI -0.5 to 0.1, P = 0.07). For pain-cases at baseline (pain intensity > = 3) the odds ratio - in the training group compared with the control group - for being a non-case at follow-up (pain intensity < 3) was 2.0 (95% CI 1.0 to 4.2) for the neck and 3.9 (95% CI 1.7 to 9.4) for the shoulders.ConclusionHigh-intensity strength training relying on principles of progressive overload can be successfully implemented at industrial workplaces, and results in significant reductions of neck and shoulder pain.Trial registrationNCT01071980.

Kettlebell training for musculoskeletal and cardiovascular health: a randomized controlled trial

OBJECTIVE The aim of this trial was to investigate the effectiveness of a worksite intervention using kettlebell training to improve musculoskeletal and cardiovascular health. METHODS This single-blind randomized controlled trial involved 40 adults from occupations with a high prevalence of reported musculoskeletal pain symptoms (mean age 44 years, body mass index 23 kg/m², 85% women, with pain intensity of the neck/shoulders 3.5 and of the low back 2.8 on a scale of 0-10). A blinded assessor took measures at baseline and follow-up. Participants were randomly assigned to training--consisting of ballistic full-body kettlebell exercise 3 times per week for 8 weeks--or a control group. The main outcome measures were pain intensity of the neck/shoulders and low back, isometric muscle strength, and aerobic fitness. RESULTS Compared with the control group, pain intensity of the neck/shoulders decreased 2.1 points [95% confidence interval (95% CI) -3.7- -0.4] and pain intensity of the low back decreased 1.4 points (95% CI -2.7- -0.02) in the training group. Compared with the control group, the training group increased muscle strength of the trunk extensors (P<0.001), but not of the trunk flexors and shoulders. Aerobic fitness remained unchanged. CONCLUSIONS Worksite intervention using kettlebell training reduces pain in the neck/shoulders and low back and improves muscle strength of the low back among adults from occupations with a high prevalence of reported musculoskeletal pain symptoms. This type of training does not appear to improve aerobic fitness.

Muscle Activation During Selected Strength Exercises in Women With Chronic Neck Muscle Pain

Background and Purpose: Muscle-specific strength training has previously been shown to be effective in the rehabilitation of chronic neck muscle pain in women. The aim of this study was to determine the level of activation of the neck and shoulder muscles using surface electromyography (EMG) during selected strengthening exercises in women undergoing rehabilitation for chronic neck muscle pain (defined as a clinical diagnosis of trapezius myalgia). Subjects: The subjects were 12 female workers (age=30–60 years) with a clinical diagnosis of trapezius myalgia and a mean baseline pain intensity of 5.6 (range=3–8) on a scale of 0 to 9. Method: Electromyographic activity in the trapezius and deltoid muscles was measured during the exercises (lateral raises, upright rows, shrugs, one-arm rows, and reverse flys) and normalized to EMG activity recorded during a maximal voluntary static contraction (MVC). Results: For most exercises, the level of muscle activation was relatively high (>60% of MVC), highlighting the effectiveness and specificity of the respective exercises. For the trapezius muscle, the highest level of muscle activation was found during the shrug (102±11% of MVC), lateral raise (97±6% of MVC), and upright row (85±5% of MVC) exercises, but the latter 2 exercises required smaller training loads (3–10 kg) compared with the shrug exercise (20–30 kg). Discussion and Conclusion: The lateral raise and upright row may be suitable alternatives to shrugs during rehabilitation of chronic neck muscle pain. Several of the strength exercises had high activation of neck and shoulder muscles in women with chronic neck pain. These exercises can be used equally in the attempt to achieve a beneficial treatment effect on chronic neck muscle pain.

Foot Medial Longitudinal-Arch Deformation During Quiet Standing and Gait in Subjects with Medial Tibial Stress Syndrome

The objective of this study was to investigate (1) if subjects with medial tibial stress syndrome demonstrate increased navicular drop and medial longitudinal-arch deformation during quiet standing and gait compared with healthy subjects, and (2) the relationship between medial longitudinal-arch deformation during quiet standing and gait. Thirty subjects aged 20 to 32 years were included (15 with medial tibial stress syndrome and 15 controls). Navicular drop and medial longitudinal-arch deformation were measured during quiet standing with neutral and loaded foot using a ruler and digital photography. Medial longitudinal-arch deformation was measured during walking gait using 3-dimensional gait analysis. Subjects with medial tibial stress syndrome demonstrated a significantly larger navicular drop (mean +/- 1 SD, 7.7 +/- 3.1 mm) and medial longitudinal-arch deformation (5.9 +/- 3.2 degrees) during quiet standing compared with controls (5.0 +/- 2.2 mm and 3.5 +/- 2.6 degrees, P < .05). Subjects with medial tibial stress syndrome also demonstrated significantly larger medial longitudinal-arch deformation (8.8 +/- 1.8 degrees) during gait compared with controls (7.1 +/- 1.7 degrees, P = .015). There was no correlation between medial longitudinal-arch deformation during quiet standing and gait in either of the 2 groups (r < 0.127, P > .653). The subjects with medial tibial stress syndrome in this study demonstrated increased navicular drop and medial longitudinal-arch deformation during quiet standing and increased medial longitudinal-arch deformation during gait compared to healthy subjects. Medial longitudinal-arch deformation during quiet standing did not correlate with medial longitudinal-arch deformation during gait in either of the 2 groups. ACFAS Level of Clinical Evidence: 5.

Rapid Hamstring/quadriceps Force Capacity in Male vs. Female Elite Soccer Players

Zebis, MK, Andersen, LL, Ellingsgaard, H, and Aagaard, P. Rapid hamstring/quadriceps force capacity in male vs. female elite soccer players. J Strength Cond Res 25(7): 1989-1993, 2011—Knee joint injuries are a serious issue in soccer. The ability to protect the knee from injury depends largely on the strength of the hamstring relatively to the quadriceps, that is, a low hamstring/quadriceps (H/Q) strength ratio is suggested as a risk factor. Although maximal muscle strength (MVC) has often been used to evaluate the H/Q ratio, the ability to rapidly develop force (rate of force development [RFD]) is more relevant in relation to fast dynamic movements. The aim of this study was to introduce and investigate a rapid RFD H/Q strength ratio compared with the traditional MVC H/Q strength ratio in elite soccer players. Twenty-three elite soccer players (11 women, 12 men) performed maximal voluntary static contraction for the hamstring and quadriceps in an isokinetic dynamometer, from which the maximal muscles strength (MVC) and RFD were extracted. Test-retest reliability for the RFD H/Q ratio was high (intraclass correlation coefficient = 0.664-0.933). The initial contraction phase up to 50 milliseconds from the onset of contraction showed a low RFD H/Q ratio compared to the MVC H/Q ratio (p < 0.001). These results suggest a reduced potential for knee joint stabilization during the very initial phase of muscle contraction. Two female players—both with a markedly low RFD H/Q ratio, but a normal MVC H/Q ratio, compared with the group mean—sustained ACL rupture at a later occasion. The high reliability of the new RFD H/Q strength ratio indicates that the method is a relevant tool in standardized clinical evaluation of the knee joint agonist-antagonist relationship.