Josefine Stoll

Validity of isokinetic trunk measurements with respect to healthy adults, athletes and low back pain patients

Background: Isokinetic measurements are widely used to assess strength capacity in a clinical or research context. Nevertheless, the validity of isokinetic measures for identifying strength deficits and the evaluation of therapeutic process regard- ing different pathologies is yet to be established. Therefore, the purpose of this review is to evaluate the validity of isokinetic measures in a specific case: that of muscular capacity in low back pain (LBP). Methods: A literature search (PubMed; ISI Web of Knowledge; The Cochrane Library) covering the last 10 years was performed. Relevant papers regarding isokinetic trunk strength measures in healthy and patients with low back pain (PLBP) were searched. Peak torque values (Nm) and peak torque normalized to body weight (Nm/kg BW) were extracted for healthy and PLBP. Ranked mean values across studies were calculated for the concentric peak torque at 60 ◦ /s as well as the flexion/extension (F/E) ratio. Results: 34 publications (31 flexion/extension; 3 rotation) were suitable for reporting detailed isokinetic strength measures in healthy or LBP (untrained adults, adolescents, athletes). Adolescents and athletes were different compared to normal adults in terms of absolute trunk strength values and the F/E ratio. Furthermore, isokinetic measures evaluating therapeutic process and isokinetic rehabilitation training were infrequent in literature (8 studies). Conclusion: Isokinetic measurements are valid for measuring trunk flexion/extension strength and F/E ratio in athletes, adoles- cents and (untrained) adults with/without LBP. The validity of trunk rotation is questionable due to a very small number of pub- lications whereas no reliable source regarding lateral flexion could be traced. Therefore, isokinetic dynamometry may be utilized for identifying trunk strength deficits in healthy adults and PLBP.

Back pain prevalence in adolescent athletes

The research aimed to investigate back pain (BP) prevalence in a large cohort of young athletes with respect to age, gender, and sport discipline. BP (within the last 7 days) was assessed with a face scale (face 1–2 = no pain; face 3–5 = pain) in 2116 athletes (m/f 61%/39%; 13.3 ± 1.7 years; 163.0 ± 11.8 cm; 52.6 ± 13.9 kg; 4.9 ± 2.7 training years; 8.4 ± 5.7 training h/week). Four different sports categories were devised (a: combat sports, b: game sports; c: explosive strength sport; d: endurance sport). Analysis was described descriptively, regarding age, gender, and sport. In addition, 95% confidence intervals (CI) were calculated. About 168 (8%) athletes were allocated into the BP group. About 9% of females and 7% of males reported BP. Athletes, 11–13 years, showed a prevalence of 2–4%; while prevalence increased to 12–20% in 14‐ to 17‐year olds. Considering sport discipline, prevalence ranged from 3% (soccer) to 14% (canoeing). Prevalences in weight lifting, judo, wrestling, rowing, and shooting were ≥10%; in boxing, soccer, handball, cycling, and horse riding, ≤6%. 95% CI ranged between 0.08–0.11. BP exists in adolescent athletes, but is uncommon and shows no gender differences. A prevalence increase after age 14 is obvious. Differentiated prevention programs in daily training routines might address sport discipline‐specific BP prevalence.

Effects of sudden walking perturbations on neuromuscular reflex activity and three-dimensional motion of the trunk in healthy controls and back pain symptomatic subjects

Background Back pain patients (BPP) show delayed muscle onset, increased co-contractions, and variability as response to quasi-static sudden trunk loading in comparison to healthy controls (H). However, it is unclear whether these results can validly be transferred to suddenly applied walking perturbations, an automated but more functional and complex movement pattern. There is an evident need to develop research-based strategies for the rehabilitation of back pain. Therefore, the investigation of differences in trunk stability between H and BPP in functional movements is of primary interest in order to define suitable intervention regimes. The purpose of this study was to analyse neuromuscular reflex activity as well as three-dimensional trunk kinematics between H and BPP during walking perturbations. Methods Eighty H (31m/49f;29±9yrs;174±10cm;71±13kg) and 14 BPP (6m/8f;30±8yrs;171±10cm;67±14kg) walked (1m/s) on a split-belt treadmill while 15 right-sided perturbations (belt decelerating, 40m/s2, 50ms duration; 200ms after heel contact) were randomly applied. Trunk muscle activity was assessed using a 12-lead EMG set-up. Trunk kinematics were measured using a 3-segment-model consisting of 12 markers (upper thoracic (UTA), lower thoracic (LTA), lumbar area (LA)). EMG-RMS ([%],0-200ms after perturbation) was calculated and normalized to the RMS of unperturbed gait. Latency (TON;ms) and time to maximum activity (TMAX;ms) were analysed. Total motion amplitude (ROM;[°]) and mean angle (Amean;[°]) for extension-flexion, lateral flexion and rotation were calculated (whole stride cycle; 0-200ms after perturbation) for each of the three segments during unperturbed and perturbed gait. For ROM only, perturbed was normalized to unperturbed step [%] for the whole stride as well as the 200ms after perturbation. Data were analysed descriptively followed by a student´s t-test to account for group differences. Co-contraction was analyzed between ventral and dorsal muscles (V:R) as well as side right:side left ratio (Sright:Sleft). The coefficient of variation (CV;%) was calculated (EMG-RMS;ROM) to evaluate variability between the 15 perturbations for all groups. With respect to unequal distribution of participants to groups, an additional matched-group analysis was conducted. Fourteen healthy controls out of group H were sex-, age- and anthropometrically matched (group Hmatched) to the BPP. Results No group differences were observed for EMG-RMS or CV analysis (EMG/ROM) (p>0.025). Co-contraction analysis revealed no differences for V:R and Srigth:Sleft between the groups (p>0.025). BPP showed an increased TON and TMAX, being significant for Mm. rectus abdominus (p = 0.019) and erector spinae T9/L3 (p = 0.005/p = 0.015). ROM analysis over the unperturbed stride cycle revealed no differences between groups (p>0.025). Normalization of perturbed to unperturbed step lead to significant differences for the lumbar segment (LA) in lateral flexion with BPP showing higher normalized ROM compared to Hmatched (p = 0.02). BPP showed a significant higher flexed posture (UTA (p = 0.02); LTA (p = 0.004)) during normal walking (Amean). Trunk posture (Amean) during perturbation showed higher trunk extension values in LTA segments for H/Hmatched compared to BPP (p = 0.003). Matched group (BPP vs. Hmatched) analysis did not show any systematic changes of all results between groups. Conclusion BPP present impaired muscle response times and trunk posture, especially in the sagittal and transversal planes, compared to H. This could indicate reduced trunk stability and higher loading during gait perturbations.

Trunk Muscle Activity during Drop Jump Performance in Adolescent Athletes with Back Pain

In the context of back pain, great emphasis has been placed on the importance of trunk stability, especially in situations requiring compensation of repetitive, intense loading induced during high-performance activities, e.g., jumping or landing. This study aims to evaluate trunk muscle activity during drop jump in adolescent athletes with back pain (BP) compared to athletes without back pain (NBP). Eleven adolescent athletes suffering back pain (BP: m/f: n = 4/7; 15.9 ± 1.3 y; 176 ± 11 cm; 68 ± 11 kg; 12.4 ± 10.5 h/we training) and 11 matched athletes without back pain (NBP: m/f: n = 4/7; 15.5 ± 1.3 y; 174 ± 7 cm; 67 ± 8 kg; 14.9 ± 9.5 h/we training) were evaluated. Subjects conducted 3 drop jumps onto a force plate (ground reaction force). Bilateral 12-lead SEMG (surface Electromyography) was applied to assess trunk muscle activity. Ground contact time [ms], maximum vertical jump force [N], jump time [ms] and the jump performance index [m/s] were calculated for drop jumps. SEMG amplitudes (RMS: root mean square [%]) for all 12 single muscles were normalized to MIVC (maximum isometric voluntary contraction) and analyzed in 4 time windows (100 ms pre- and 200 ms post-initial ground contact, 100 ms pre- and 200 ms post-landing) as outcome variables. In addition, muscles were grouped and analyzed in ventral and dorsal muscles, as well as straight and transverse trunk muscles. Drop jump ground reaction force variables did not differ between NBP and BP (p > 0.05). Mm obliquus externus and internus abdominis presented higher SEMG amplitudes (1.3–1.9-fold) for BP (p < 0.05). Mm rectus abdominis, erector spinae thoracic/lumbar and latissimus dorsi did not differ (p > 0.05). The muscle group analysis over the whole jumping cycle showed statistically significantly higher SEMG amplitudes for BP in the ventral (p = 0.031) and transverse muscles (p = 0.020) compared to NBP. Higher activity of transverse, but not straight, trunk muscles might indicate a specific compensation strategy to support trunk stability in athletes with back pain during drop jumps. Therefore, exercises favoring the transverse trunk muscles could be recommended for back pain treatment.

Trunk extensor and flexor strength capacity in healthy young elite athletes aged 11-15 years.

Abstract Mueller, J, Mueller, S, Stoll, J, Baur, H, and Mayer, F. Trunk extensor and flexor strength capacity in healthy young elite athletes aged 11–15 years. J Strength Cond Res 28(5): 1328–1334, 2014—Differences in trunk strength capacity because of gender and sports are well documented in adults. In contrast, data concerning young athletes are sparse. The purpose of this study was to assess the maximum trunk strength of adolescent athletes and to investigate differences between genders and age groups. A total of 520 young athletes were recruited. Finally, 377 (n = 233/144 M/F; 13 ± 1 years; 1.62 ± 0.11 m height; 51 ± 12 kg mass; training: 4.5 ± 2.6 years; training sessions/week: 4.3 ± 3.0; various sports) young athletes were included in the final data analysis. Furthermore, 5 age groups were differentiated (age groups: 11, 12, 13, 14, and 15 years; n = 90, 150, 42, 43, and 52, respectively). Maximum strength of trunk flexors (Flex) and extensors (Ext) was assessed in all subjects during isokinetic concentric measurements (60°·s−1; 5 repetitions; range of motion: 55°). Maximum strength was characterized by absolute peak torque (Flexabs, Extabs; N·m), peak torque normalized to body weight (Flexnorm, Extnorm; N·m·kg−1 BW), and Flexabs/Extabs ratio (RKquot). Descriptive data analysis (mean ± SD) was completed, followed by analysis of variance (&agr; = 0.05; post hoc test [Tukey-Kramer]). Mean maximum strength for all athletes was 97 ± 34 N·m in Flexabs and 140 ± 50 N·m in Extabs (Flexnorm = 1.9 ± 0.3 N·m·kg−1 BW, Extnorm = 2.8 ± 0.6 N·m·kg−1 BW). Males showed statistically significant higher absolute and normalized values compared with females (p < 0.001). Flexabs and Extabs rose with increasing age almost 2-fold for males and females (Flexabs, Extabs: p < 0.001). Flexnorm and Extnorm increased with age for males (p < 0.001), however, not for females (Flexnorm: p = 0.26; Extnorm: p = 0.20). RKquot (mean ± SD: 0.71 ± 0.16) did not reveal any differences regarding age (p = 0.87) or gender (p = 0.43). In adolescent athletes, maximum trunk strength must be discussed in a gender- and age-specific context. The Flexabs/Extabs ratio revealed extensor dominance, which seems to be independent of age and gender. The values assessed may serve as a basis to evaluate and discuss trunk strength in athletes.

Back Pain in Adolescent Athletes: Results of a Biomechanical Screening

The aim was to use a short biomechanical test battery to screen adolescent athletes with and without back pain to reveal relevant and possibly preventable deficits. 1 559 adolescent athletes (m/f 945/614; 13.2±1.6y) were included. Back pain was assessed (1–5: 1=no pain; 5=maximum pain) for dichotomous categorization into back pain (BP: pain>2, n=113), healthy (NBP All : pain=1, n=1 213) and matched healthy (NBP matched : pain=1, n=113) athletes. Athletes performed stability, performance (jumps) and trunk strength testing. The center of pressure displacement [mm], jump height [cm], peak force [N], contact time [ms] and peak torque of the trunk [Nm] were analyzed. Analysis showed a statistically significant influence of trunk strength on back pain (BP/NBP ALL ). Nevertheless, after including co-variables (anthropometrics, gender and training volume), there were no significant variables detectable any longer. ANOVA identified no group differences (BP/NBP matched ) in the outcome measurement for the biomechanical tests (p>0.05). This short biomechanical screening shows no sufficient differentiation in adolescent athletes for back pain. Therefore, age, training load and gender has greater relevance than strength deficits or postural control. This is challenging for further understanding of the complex conditions in young athletes with back pain.

EFFECTS OF ADDITIONAL PERTURBATION ON NEUROMUSCULAR TRUNK ACTIVATION PATTERN DURING CORE-SPECIFIC SENSORIMOTOR EXERCISE

Background Sensorimotor exercises (SE) are evident to enhance neuromuscular activity of the trunk muscles (TM). However, it is unclear if an additional unexpected perturbation leads to higher muscular activity and therefore enhances training efficacy. Objective To analyse effects of additional unexpected perturbations on trunk neuromuscular activation pattern during SE. Design Cross-sectional design. Setting University Outpatient Clinic, Sports Medicine Centre. Participants Ten healthy, normal active participants (5 m/5 f; 29±2 yrs; 177±7 cm, 74±12 kg) were included. Assessment of Risk Factors All participants were prepared with a bilateral 12-lead trunk EMG (Mm. rectus abdominis (RA), external obliquus (EO), internal obliquus (IO), latissimus dorsi (LD), thoracic (UES) and lumbar erector spinae (LES)). Warm-up on an isokinetic dynamometer (extension/flexion; 30 rep; 60°sec) was followed by maximum voluntary isometric contraction measurements (MVC, 5 sec). Next, a (right-armed) side plank on stable surface (SP; 30 sec) and 2 different instable conditions were randomly assigned (SP plus pad under the elbow (SPP), SPP plus perturbation (SPP+P)). Main Outcome Measurements Root mean square (RMS) normalized to MVC (%MVC) was calculated during the whole exercise. Muscles were grouped to ventral right/left (VR;VL=mean of RA, IO, EO), and dorsal right/left (DR;DL=mean of LD, UES, LES). Differences between conditions were calculated for muscle groups, Ventral:Dorsal (V:D) and Side-Right/Side-Left ratio (SR;SL) (repeated-measures ANOVA; α=0.05). Results SPP+P showed highest EMG-RMS (e.g,VR: 81±9%; DR: 55±12%) for all muscle groups except DL with significant differences (p<0.05) between conditions SP and SPP+P in VR, VL and DR muscle groups. No differences were found between SPP (e.g.,VR: 71±11%) and SPP+P (e.g.,VR: 81±9%)(p>0.05). Statistically significant higher V:D ratios was found in SPP+P compared to SP (p<0.05). SR:SL ratio did not show any differences (p>0.05). Conclusions The use of additional perturbations during core stability training is superior to enhance trunk neuromuscular activity and should be implemented into sensorimotor exercises addressing the trunk.

BACK PAIN RISK FACTORS IN ADOLESCENT ATHLETES: SUITABILITY OF A BIOMECHANICAL SCREENING TOOL?

Background Back pain (BP) is already a relevant injury site in adolescent athletes. A valid screening is essential for BP prevention. Objective To investigate whether a biomechanical screening tool (BST) is suitable to predict BP in adolescent athletes. Design Longitudinal analysis with 1.9±1.0 yrs between both measurement days. Setting Medical center of the German Olympic Sports Federation. BST was implemented in the annual (pre-participation) examination of elite athletes. Patients (or Participants) 343 athletes (195 males/148 females, 13±1 yrs, 164±12 cm, 53±13 kg, 5±3 training years, 8±6 training hours per week) out of 20 sport disciplines were included in the study. Interventions (or Assessment of Risk Factors) Subjective BP was assessed using a faces-pain-scale (FPS 1–5: 1=no pain; 2–5=slight- to maximum pain). In addition, postural control (one-legged stance), jumping performance (counter movement/drop jump), and maximum isokinetic trunk extension/flexion strength (60°/sec) was assessed for all athletes. Main Outcome Measurements Athletes were classified into 4 groups with respect to the course of back pain [(A) no BP (n=206); (B) BP-developers (n=34); (C) persisting BP (n=71); (D) diminishing BP (n=32)]. Outcomes included center of pressure displacement COP [mm], jump height [cm], peak jumping force [N], contact time [ms] and peak torque for trunk extension/flexion [Nm]. Descriptive analysis was followed by two-way ANOVA (repeated measures; α=0.05). Results Overall, the athletes enhanced trunk strength, jump performance and postural control across the evaluation period. Pain free athletes (A) showed statistically significant higher trunk strength gains (extension/flexion: +45/+37%) compared to athletes developing BP (B: +20/+9%; p<0.05). No differences were observed for jump performance and postural control (p>0.05). Conclusions Analysing biomechanical variables is valid to identify significantly impaired trunk strength development in athletes with BP incidence. In contrast, jump performance and postural control are of minor relevance. Therefore, poor trunk strength development could serve as back pain risk factor in athletes. Trunk strength training interventions should be recommended.

Influence of load on three-dimensional segmental trunk kinematics in one-handed lifting: A pilot study

Stability of the trunk is relevant in determining trunk response to different loading in everyday tasks initiated by the limbs. Descriptions of the trunks mechanical movement patterns in response to different loads while lifting objects are still under debate. Hence, the aim of this study was to analyze the influence of weight on 3-dimensional segmental motion of the trunk during 1-handed lifting. Ten asymptomatic subjects were included (29 ± 3 y; 1.79 ± 0.09 m; 75 ± 14 kg). Subjects lifted 3× a light and heavy load from the ground up onto a table. Three-dimensional segmental trunk motion was measured (12 markers; 3 segments: upper thoracic area [UTA], lower thoracic area [LTA], lumbar area [LA]). Outcomes were total motion amplitudes (ROM;[°]) for anterior flexion, lateral flexion, and rotation of each segment. The highest ROM was observed in the LTA segment (anterior flexion), and the smallest ROM in the UTA segment (lateral flexion). ROM differed for all planes between the 3 segments for both tasks (P < .001). There were no differences in ROM between light and heavy loads (P > .05). No interaction effects (load × segment) were observed, as ROM did not reveal differences between loading tasks. Regardless of weight, the 3 segments did reflect differences, supporting the relevance of multisegmental analysis.

General versus sports-specific injury prevention programs in athletes: A systematic review on the effect on injury rates

Introduction Annually, 2 million sports-related injuries are reported in Germany of which athletes contribute to a large proportion. Multiple sport injury prevention programs designed to decrease acute and overuse injuries in athletes have been proven effective. Yet, the programs’ components, general or sports-specific, that led to these positive effects are uncertain. Despite not knowing about the superiority of sports-specific injury prevention programs, coaches and athletes alike prefer more specialized rather than generalized exercise programs. Therefore, this systematic review aimed to present the available evidence on how general and sports-specific prevention programs affect injury rates in athletes. Methods PubMed and Web of Science were electronically searched throughout April 2018. The inclusion criteria were publication dates Jan 2006–Dec 2017, athletes (11–45 years), exercise-based injury prevention programs and injury incidence. The methodological quality was assessed with the Cochrane Collaboration assessment tools. Results Of the initial 6619 findings, 15 studies met the inclusion criteria. In addition, 13 studies were added from reference lists and external sources making a total of 28 studies. Of which, one used sports-specific, seven general and 20 mixed prevention strategies. Twenty-four studies revealed reduced injury rates. Of the four ineffective programs, one was general and three mixed. Conclusion The general and mixed programs positively affect injury rates. Sports-specific programs are uninvestigated and despite wide discussion regarding the definition, no consensus was reached. Defining such terminology and investigating the true effectiveness of such IPPs is a potential avenue for future research.