Factors influencing bilateral deficit and inter-limb asymmetry of maximal and explosive strength: motor task, outcome measure and muscle group

Effects of Soccer Match-Play on Muscle Strength, Physical Performance, and Perceptual Responses in Elite Female Players

ABSTRACT

Gereduz Agapito, L, Brownstein, CG, and Maffiuletti, NA. Effects of soccer match-play on muscle strength, physical performance, and perceptual responses in elite female players. J Strength Cond Res 39(1): 79-85, 2025-The purpose of this study was to investigate the impact of actual soccer match-play on muscle strength, physical performance, and perceptual responses in elite female players. Twelve Swiss elite players were tested before (pre), after (post) and 48 hours after a 90-minute soccer match for knee and hip muscle strength, vertical jump height, and sprint time. Perceptual responses were also evaluated up to 72 hours postmatch with a self-reported questionnaire. Muscle strength, jump, and sprint performance were impaired at post compared with pre (p < 0.001), but fully recovered at 48 hours. Percent strength losses were higher for knee flexors (∼20%) compared with both hip adductors (∼12%; p = 0.005) and abductors (8-12%; p < 0.001), and for knee extensors compared with hip abductors (p = 0.013). Regardless of muscle group, strength losses were higher on the dominant than on the nondominant side (p = 0.010). Most perceptual responses were altered after the match (p < 0.001) and some items such as motivation to train and readiness to play remained unrecovered at 72 hours (p < 0.01). Soccer match-play induced a significant decline of knee and hip muscle strength in elite female players that was more marked for knee flexors than for hip muscles. This was accompanied by performance impairments and by altered perceptual responses that still persisted 72 hours after the match. These findings offer implications for the optimization of postmatch recovery strategies in elite female soccer players.

A practitioner's guide to isometric hip adduction and abduction test selection: Maximal force, asymmetry, and muscle activity comparisons between assessment positions

The purpose of this study was to compare maximal adduction (ADD) and abduction (ABD) force, ADD to ABD ratio (ADD:ABD), inter-limb asymmetries and muscle activity between five isometric hip strength assessment positions. Twenty male athletes performed the following positions: seated (SE), supine at knees with 0° hip flexion (SK0°) and 45° hip flexion (SK45°), and supine at ankles bilaterally (SABI) and unilaterally (SAUNI). Normalised muscle activity (%EMGmax) of adductor longus (ADDLONG), gracilis (GRAC), gluteus medius (GMED), sartorius (SAR), and lower rectus abdominis (RECABD) were also assessed. Significant main effects of assessment position were identified for relative peak force (rPF) and torque (rT), ADD:ABD, ADD asymmetry, and %EMGmax. Significantly greater ADD and ABD rPF and rT were observed in SE and SK45° compared to SABI and SAUNI. SK45° elicited the highest ADDLONG and GRAC %EMGmax during ADD, with SE and SK45° evoking the highest GMED %EMGmax during ABD. SK0° exhibited significantly higher ADD:ABD compared to all positions except SAUNI. ADD asymmetry was significantly largest in SAUNI, and RECABD %EMGmax was highest in SABI during ADD. This data can inform selection of assessment positions based on whether the primary measures of interest are maximal force and muscle activity, or identifying asymmetries.

Longitudinal Monitoring of Biomechanical and Psychological State in Collegiate Female Basketball Athletes Using Principal Component Analysis

Background

The growth in participation in collegiate athletics has been accompanied by increased sport-related injuries. The complex and multifactorial nature of sports injuries highlights the importance of monitoring athletes prospectively using a novel and integrated biopsychosocial approach, as opposed to contemporary practices that silo these facets of health.

Methods

Data collected over two competitive basketball seasons were used in a principal component analysis (PCA) model with the following objectives: (i) investigate whether biomechanical PCs (i.e., on-court and countermovement jump (CMJ) metrics) were correlated with psychological state across a season and (ii) explore whether subject-specific significant fluctuations could be detected using minimum detectable change statistics. Weekly CMJ (force plates) and on-court data (inertial measurement units), as well as psychological state (questionnaire) data, were collected on the female collegiate basketball team for two seasons.

Results

While some relationships (n = 2) were identified between biomechanical PCs and psychological state metrics, the magnitude of these associations was weak (r = |0.18-0.19|, p < 0.05), and no other overarching associations were identified at the group level. However, post-hoc case study analysis showed subject-specific relationships that highlight the potential utility of red-flagging meaningful fluctuations from normative biomechanical and psychological patterns.

Conclusion

Overall, this work demonstrates the potential of advanced analytical modeling to characterize components of and detect statistically and clinically relevant fluctuations in student-athlete performance, health, and well-being and the need for more tailored and athlete-centered monitoring practices.

Exploring the relationship between lower limb strength, strength asymmetries, and curvilinear sprint performance: Findings from a pilot study

Team sports involve various sprinting actions, including curvilinear sprints, yet their neuromuscular factors have been understudied. The aim of this cross-sectional study was to investigate the relationship between lower limb muscle strength, strength asymmetries, linear sprint and curvilinear sprint performance. At two visits 12 male (age: 24.8 ± 4.7 years, height: 1.82 ± 0.06 m, body mass: 80 ± 6.58 kg) and 6 female (age: 20.8 ± 1.33 years, body height: 1.60 ± 0.02 m, body mass: 55.3 ± 2.88 kg) student-athletes completed isometric strength measurements of the knee flexors (KF), knee extensors (KE), hip abductors (HABD), hip adductors (HADD), as well as linear sprint and curvilinear sprint to the right and left. Sprint split times over 30 m (t30) were measured and curvilinear sprint split time deficits (t30deficit) and inter-limb strength asymmetries were calculated. Very large negative correlations were observed between HADD and HABD strength on one side and t30 of curvilinear sprint to the left (r = -0.75 and -0.71; p < 0.001) and right (ρ = -0.81 and -0.70; p < 0.001) on the other. The regression model consisting of HADD, HABD, and KF explained 76% and 67% of the variance in left and right curvilinear sprint t30, respectively. Similarly, 59% of the left curvilinear sprint t30deficit variance was explained by the HABD and KF strength. High inter-limb HABD strength symmetry was related to better left and right curvilinear sprint t30 (r = 0.71 and ρ = 0.75, p < 0.001). These results highlight the pivotal role of hip strength for curvilinear sprint speed, and emphasize the need of symmetrical HABD muscle strength to optimize neuromuscular function during curvilinear sprint.

Bilateral Force Deficit in Proximal Effectors Versus Distal Effectors in Lower Extremities

Purpose: Bilateral force deficit occurs when the maximal generated force during simultaneous bilateral muscle contractions is lower than the sum of forces generated unilaterally. Neural inhibition is stated as the main source for bilateral force deficit. Based on differences in bilateral neural organization, there might be a pronounced neural inhibition for proximal compared to distal effectors. The aim of the present experiment was to evaluate potential differences in bilateral force deficit in proximal compared to distal effectors in lower extremities. Methods: Fifteen young adults performed single-joint maximal voluntary contractions in isometric dorsiflexion of ankle (distal) and knee (proximal) extension unilaterally and bilaterally. Results: Results showed a significant absolute bilateral force deficit for both proximal (123.46 ± 59.51 N) and distal effectors (33.00 ± 35.60 N). Interestingly, the relative bilateral force deficit for knee extension was significantly larger compared to dorsiflexion of ankle, 19.98 ± 10.04% and 10.27 ± 9.57%, respectively. Our results indicate a significantly higher bilateral force deficit for proximal effectors compared to distal effectors. Conclusion: Plausible explanations are related to neuroanatomical and neurophysiological differences between proximal effectors and distal effectors where proximal muscles have a higher potential for bilateral communication compared to distal muscles. In addition, higher forces produced with proximal effectors could cause a higher perceived exertion and cause a more pronounced bilateral force deficit to proximal effectors.

Monitoring lower limb biomechanical asymmetry and psychological measures in athletic populations-A scoping review

BACKGROUND

Lower limb biomechanics, including asymmetry, are frequently monitored to determine sport performance level and injury risk. However, contributing factors extend beyond biomechanical and asymmetry measures to include psychological, sociological, and environmental factors. Unfortunately, inadequate research has been conducted using holistic biopsychosocial models to characterize sport performance and injury risk. Therefore, this scoping review summarized the research landscape of studies concurrently assessing measures of lower limb biomechanics, asymmetry, and introspective psychological state (e.g., pain, fatigue, perceived exertion, stress, etc.) in healthy, competitive athletes.

METHODS

A systematic search of MEDLINE, Embase, CINAHL, SPORTDiscus, and Web of Science Core Collections was designed and conducted in accordance with PRISMA guidelines. Fifty-one articles were included in this review.

RESULTS

Significant relationships between biomechanics (k = 22 studies) or asymmetry (k = 20 studies) and introspective state were found. Increased self-reported pain was associated with decreased range of motion, strength, and increased lower limb asymmetry. Higher ratings of perceived exertion were related to increased lower limb asymmetry, self-reported muscle soreness, and worse jump performance. Few studies (k = 4) monitored athletes longitudinally throughout one or more competitive season(s).

CONCLUSION

This review highlights the need for concurrent analysis of introspective, psychological state, and biomechanical asymmetry measures along with longitudinal research to understand the contributing factors to sport performance and injury risk from biopsychosocial modeling. In doing so, this framework of biopsychosocial preventive and prognostic patient-centered practices may provide an actionable means of optimizing health, well-being, and sport performance in competitive athletes.

The Influence of Quadriceps Strength and Rate of Torque Development on the Recovery of Knee Biomechanics During Running After Anterior Cruciate Ligament Reconstruction

BACKGROUND

After anterior cruciate ligament reconstruction (ACLR), altered surgical knee biomechanics during running is common. Although greater quadriceps strength is associated with more symmetrical running knee kinetics after ACLR, abnormal running mechanics persist even after resolution of quadriceps strength deficits. As running is a submaximal effort task characterized by limited time to develop knee extensor torque, quadriceps rate of torque development (RTD) may be more closely associated with recovery of running knee mechanics than peak torque (PT).

PURPOSE

To assess the influence of recovery in quadriceps PT and RTD symmetry on knee kinematic and kinetic symmetry during running over the initial 2 years after ACLR.

STUDY DESIGN

Cohort study; Level of evidence, 3.

METHODS

A total of 39 Division I collegiate athletes (106 testing sessions; 19 female) completed serial isometric performance testing and running analyses between 3 and 24 months after ACLR. Athletes performed maximal and rapid isometric knee extension efforts with each limb to assess PT and RTD between-limb symmetry indices (PTLSI and RTDLSI), respectively. Peak knee flexion difference (PKFDIFF) and peak knee extensor moment limb symmetry index (PKEMLSI) during running were computed. Multivariable linear mixed-effects models assessed the influence of PTLSI and RTDLSI on PKFDIFF and PKEMLSI over the initial 2 years after ACLR.

RESULTS

Significant main effects of RTDLSI (P < .001) and time (P≤ .02) but not PTLSI (P≥ .24) were observed for both PKFDIFF and PKEMLSI models. For a 10% increase in RTDLSI, while controlling for PTLSI and time, a 0.9° (95% CI, 0.5°-1.3°) reduction in PKFDIFF and a 3.5% (95% CI, 1.9%-5.1%) increase in PKEMLSI are expected. For every month after ACLR, a 0.2° (95% CI, 0.1°-0.4°) reduction in PKFDIFF and a 1.3% (95% CI, 0.6%-2.0%) increase in PKEMLSI are expected, controlling for PTLSI and RTDLSI.

CONCLUSION

Quadriceps RTDLSI was more strongly associated with symmetrical knee biomechanics during running compared with PTLSI or time throughout the first 2 years after ACLR.

Hip Strength Profiling of Ice Hockey Athletes Across Various Joint-Specific Angles: Monitoring and Injury Implications

ABSTRACT

Secomb, JL, Kelly, M, and Dascombe, BJ. Hip strength profiling of ice hockey athletes across various joint-specific angles: monitoring and injury implications. J Strength Cond Res 37(7): e422-e429, 2023-The purpose of this research was to compare the hip adduction and abduction relative strength, adduction-to-abduction strength ratio (ADD:ABD), and interlimb asymmetries of ice hockey athletes between the typically used bilateral position and 3 unilateral positions in joint-specific angles (0°, 25°, and 50° of hip abduction) relevant to an ice hockey stride. A secondary purpose was to explore any relationships between these measures and hip and groin noncontact injuries, and self-reported pain and disability. Twenty-five semiprofessional male ice hockey athletes (26.7 ± 6.7 years) were assessed for hip abduction range of motion (ROM), hip adduction and abduction relative strength, and completed the Copenhagen Hip and Groin Outcome Score (HAGOS) questionnaire. Within-subjects repeated-measures analysis of variance revealed a significant effect for the assessment position for adduction ( F1,24 = 52.4, p < 0.01) and abduction relative strength ( F1,24 = 152.1, p < 0.01), ADD:ABD ( F1,24 = 38.9, p < 0.01), and the interlimb asymmetries for each of these variables ( F1,24 = 9.8-12.3; p < 0.01), with large strength differences observed between the bilateral assessment and all unilateral assessment positions for adduction and abduction relative strength. In addition, 4 athletes experienced a noncontact hip or groin injury within 1 month after testing, and when compared with the rest of the cohort ( n = 21) with Welch's t -tests, demonstrated significantly reduced hip abduction ROM (mean difference [MD] = -8.4 ± 2.5°; p < 0.01), sport subscale score for the HAGOS questionnaire (MD = -33.9 ± 7.1; p < 0.01), and a decline in hip adduction relative strength in the unilateral position of 50° compared with the position of 25° hip abduction (MD = -13.4 ± 3.8; p = 0.04). These results suggest that practitioners working with ice hockey athletes may benefit from profiling hip strength in these unilateral joint-specific angle positions because they provide an evidence base to determine the hip strength needs of ice hockey athletes in positions associated with skating performance and noncontact hip and groin injury mechanisms (between 25° and 50° of hip abduction).

Assessment of asymmetry at different intensities between conventional and paralympic powerlifting athletes

Powerlifting competitions require consistent and symmetric lifting of heavy loads and maximal effort, in which, asymmetric lifting results in trial invalidation. Symmetry during this very high intensity movement is determinant to athletes' performance and success in competitions. This study aimed to compare the asymmetry between Conventional Powerlifting athletes (CP) and Paralympic (PP) athletes at intensities of 45 and 80% 1RM before and after a training session. Twenty-two male athletes (11 CP: 29.84 ± 4.21 and 11 PP: 30.81 ± 8.05 years old) participated in this study. Mean Propulsive Velocity (MPV), Maximum Velocity (Vmax) and Power during the concentric and eccentric phases were evaluated at 45%-1RM before and after a training session. For the intensity of 80%-1RM, MPV, Vmax and Power were measured in the first and last series (5 series of 5 repetitions: 5X5) of a training session. PP athletes demonstrated lower velocity and greater symmetry at 45%-1RM, but higher velocity and less asymmetry at 80%-1RM, when compared to CP. The data indicated that PP athletes tend to be slower at lower intensities, faster at higher intensities in absolute values, and have greater symmetry than CP.

Long-Term Muscular Atrophy and Weakness Following Cessation of Botulinum Toxin Type A Injections in the Flexor Digitorum Muscle of Musicians with Focal Hand Dystonia

The present study assessed muscular atrophy and weakness of the flexor digitorum superficialis (FDS) and profundus (FDP) muscle as possible long-term side effects of botulinum toxin (BoNT) injections in hand dystonia patients after the termination of their treatment. For the assessment of both parameters, a group of 12 musicians diagnosed with focal hand dystonia was compared with a group of 12 healthy matched musicians. The minimum and maximum times since the last injection across patients were 0.5 to 3.5 years, respectively. The thickness and strength of the FDS and FDP were assessed via ultrasonography and a strength measurement device. Group differences were estimated through the calculation of the symmetry index between the dominant and non-dominant hand. The results revealed that compared to the control group, thickness and flexion strength of the injected FDS and FDP were decreased by 10.6% ± 5.3% (95% CI) and 12.5% ± 6.4% (95% CI), respectively, in the patient group. The amount of weakness and atrophy was predicted significantly by the total amount of BoNT injected throughout the entire treatment period. In contrast, the time after the last injection did not predict the amount of strength and muscle mass recovery after the cessation of the treatment. The current study revealed that even up to 3.5 years after the termination of BoNT injections, long-term side effects such as weakness and atrophy can still be observed. We suggest that the total BoNT dose should remain as small as possible to reduce long-lasting side effects to the minimum. Although side effects differ significantly among patients, a potential full recovery of atrophy and weakness after the cessation of BoNT treatment might be observed after periods longer than 3.5 years.

Seasonal Variation of Physical Performance, Bilateral Deficit, and Interlimb Asymmetry in Elite Academy Soccer Players: Which Metrics Are Sensitive to Change?

ABSTRACT

Bishop, C, Abbott, W, Brashill, C, Loturco, I, Beato, M, and Turner, A. Seasonal variation of physical performance, bilateral deficit, and interlimb asymmetry in elite academy soccer players: Which metrics are sensitive to change? J Strength Cond Res 37(2): 358-365, 2023-This study aimed to report seasonal variations for (a) physical performance, (b) interlimb asymmetry, and (c) bilateral deficit (BLD) data over the course of a competitive soccer season and determine which metrics are sensitive to change. This study used a repeated-measures observational design for 19 under-20, elite, academy, soccer players (age: 17.58 ± 0.61 years; height: 1.81 ± 0.09 m; body mass: 74.36 ± 7.58 kg), who conducted bilateral and single-leg countermovement jumps (CMJ and SLCMJ), linear speed (5, 10, 20, and 30-m) and 505 change of direction (COD) speed tests, at pre, mid, and end of season time points. For jump tests, jump height, reactive strength index modified, time to takeoff, and countermovement depth metrics were monitored, with interlimb asymmetry and the BLD also calculated for each. Significant improvements ( p < 0.05) in performance were evident in all fitness tests: CMJ (effect size [ES]: 0.61 to 1.03), SLCMJ (ES: 0.60 to 2.25), linear speed (ES: -0.54 to -1.96), and COD speed (ES: -0.68 to -1.14). Significant reductions in asymmetry (ES: -0.68 to -1.07) and significant increases in the BLD (ES: 1.15 to 1.57) were also evident throughout the season. Additionally, kappa coefficients were used to determine consistency in limb dominance throughout the season, but only poor to fair levels of agreement (kappa: -0.17 to 0.37) were evident, highlighting the fluctuating nature of limb dominance throughout the season. Despite all tests exhibiting meaningful change, the SLCMJ and linear speed showed the most frequent and largest differences in performance, highlighting their usefulness in the ongoing monitoring process of physical capacities in elite male academy players across a competitive soccer season.

Personalized volumetric assessment of lower body muscles in patients with knee injuries: A descriptive case series

BACKGROUND

Patients with knee joint pathology present with variable muscular responses across the muscles of the lower limb and pelvis. Conventional approaches to characterizing muscle function are limited to gross strength assessments that may overlook subtle changes both in the thigh, hip and shank musculature.

PURPOSE

To describe individualized patterns of lower extremity muscle volumes in patients with knee pathologies.

METHODS

This was a retrospective case series performed in a University medical center. Nine patients diagnosed with meniscus tear recommended to undergo meniscectomy volunteered. Participants underwent 3.0 Tesla magnetic resonance imaging (MRI) of the lower extremities. Thirty-five MRI-derived muscle volumes were compared between limbs and expressed as percentage asymmetry. For additional context, z-scores were also calculated for mass- and height-normalized muscles and pre-determined muscle groupings relative to a normative database.

RESULTS

There were no consistent patterns observed when considering between-limb asymmetries among all patients. The ankle musculature (dorsiflexors, plantar flexors, and invertors) was the only muscle group to be consistently smaller than normal for all patients, with the psoas major and flexor hallucis longus being the only individual muscles. The severity or chronicity of injury and presence of surgical intervention did not appear to have a clear effect on muscle volumes.

CONCLUSION

Patients with a history of meniscal pathology demonstrate inconsistent patterns of lower extremity muscle volumes about the hip, knee, and ankle between limbs and in comparison to uninjured individuals. These data support the need for individualized assessment and intervention in this population.

The Ecological Validity of Countermovement Jump to On-Court Asymmetry in Basketball

Jump-based asymmetry is often used as an indicator of sport performance and may be used to discern injury susceptibility. Due to task specificity, however, countermovement jump asymmetry may not be representative of on-court asymmetry. As such, we assessed the association between countermovement jump asymmetry and on-court impact asymmetry metrics (n=3, and n=4, respectively) using linear regressions (α=0.05). Fifteen female basketball athletes completed countermovement jump and on-court sessions across a competitive season. A significant negative association was found between peak landing force asymmetry and both overall and medium acceleration on-court asymmetry (b=–0.1, R ² =0.08, p<0.001; b=–0.1, R ² =0.11, p<0.001, respectively), as well as between peak propulsive force asymmetry and on-court medium acceleration asymmetry (b=–0.24, R ² =0.04, p=0.01). Alternatively, both peak landing and peak propulsive force asymmetry were significantly positively associated with on-court high acceleration asymmetry (b=0.17, R ² =0.08, p<0.001; b=0.35, R ² =0.02, p=0.04, respectively). While some overlap may exist, countermovement jump and on-court impact asymmetry appear to be independent. Thus, sport-specific monitoring may be necessary to adequately monitor injury susceptibility using asymmetry.

The Association between Bilateral Deficit and Athletic Performance: A Brief Review

An abundance of information can be found in the scientific literature regarding the bilateral deficit (BLD) in different contraction types, including its possible underlying mechanisms. On the other hand, studies on the relationship between BLD and athletic performance have only begun to emerge in recent years. The purpose of this review article is to assemble and analyze the literature on the topic of the relationship between BLD and athletic performance. After a detailed review of the scientific databases, we analyzed 10 relevant scientific articles. BLD calculated from outcomes of vertical jumps was positively related to the ability to change direction quickly in volleyball, basketball, tennis and student population, but not in soccer. Sprint running performance does not seem to be associated with BLD, while one study suggested that a smaller BLD is associated with a more efficient start in a sprint. Apart from the associations with change in direction performance, there is little evidence to support the association between BLD and athletic performance; thus, further research is required in other sports, incorporating sport-specific performance outcomes and multiple tasks to calculate the BLD.

Strength Asymmetries Are Muscle-Specific and Metric-Dependent

We investigated if dominance affected upper limbs muscle function, and we calculated the level of agreement in asymmetry direction across various muscle-function metrics of two heterologous muscle groups. We recorded elbow flexors and extensors isometric strength of the dominant and non-dominant limb of 55 healthy adults. Participants performed a series of explosive contractions of maximal and submaximal amplitudes to record three metrics of muscle performance: maximal voluntary force (MVF), rate of force development (RFDpeak), and RFD-Scaling Factor (RFD-SF). At the population level, the MVF was the only muscle function that showed a difference between the dominant and non-dominant sides, being on average slightly (3–6%) higher on the non-dominant side. At the individual level, the direction agreement among heterologous muscles was poor for all metrics (Kappa values ≤ 0.15). When considering the homologous muscles, the direction agreement was moderate between MVF and RFDpeak (Kappa = 0.37) and low between MVF and RFD-SF (Kappa = 0.01). The asymmetries are muscle-specific and rarely favour the same side across different muscle-performance metrics. At the individual level, no one side is more performative than the other: each limb is favoured depending on muscle group and performance metric. The present findings can be used by practitioners that want to decrease the asymmetry levels as they should prescribe specific exercise training for each muscle.

Maximal vs. explosive knee extensor strength in professional soccer players: inter-limb asymmetries and relationship with knee function

AbstractThe main aims of this study were to compare the magnitude of inter-limb asymmetry (ILA) and the relation with self-reported knee function between maximal and explosive knee extensor strength outcomes in professional soccer players. Forty-six male soccer players completed different maximal isokinetic and isometric contractions of the knee extensors for the assessment of maximal strength (peak torque and maximal voluntary contraction (MVC) torque) and explosive strength (early, intermediate, late, and peak rate of torque development (RTD)). Self-reported knee function was assessed with the International Knee Documentation Committee (IKDC) and Lysholm knee scoring scales. Peak torque and MVC torque showed comparable ILAs (8-9%), both being significantly lower than all RTD ILAs (16% on average; p < 0.001). ILAs for early RTD (21%) and peak RTD (19%) were significantly higher than all the other variables (p < 0.05). Only early and intermediate RTD were significantly correlated - though weakly - with both IKDC (rho = 0.32 for both) and Lysholm (rho = 0.36 and 0.30, respectively) scores. We conclude that explosive knee extensor strength - early RTD in particular - exhibited larger ILAs and better relations with self-reported knee function than peak torque and MVC torque in professional soccer players. These results confirm the validity and functional relevance of early RTD and the need for its inclusion in routine performance testing for soccer players.

Bilateral deficit magnitude increases with velocity during a half-squat exercise

Movement velocity has been viewed as one of the bilateral deficit (BLD) determinants. This research tested the velocity effect on BLD during a half-squat exercise. The role of muscle excitation in BLD was also assessed. BLD amplitude was assessed in 12 male soccer players while performing a half-squat exercise with incremental load. During the exercise's pushing phase, the average force and velocity were measured in bilateral and unilateral conditions to provide the bilateral index (BI) at each interpolated velocity. The vastus lateralis and medialis excitation was assessed during the exercise by calculating the surface electromyography signal root mean square (sEMG_RMS). The BI for sEMG_RMS (sEMG BI) was calculated. The theoretical maximum force (F₀) and velocity (v₀) were also determined. F₀ was +43 (28)% in bilateral compared with unilateral conditions (p < 0.001), whereas v₀ was similar in both conditions (p = 0.386). The BI magnitude rose with the increase in velocity from -34 (7)% at 50%v₀ to -70 (17)% at 90%v₀ (p 0.03-<0.001), whereas no sEMG BI occurred (p: 0.07-0.991 in both muscles). The study reported velocity-dependent changes in the BLD amplitude, with the largest BLD amplitudes occurring at the highest velocities. This behaviour could provide useful information for setting specific contraction velocities to exploit/limit the BLD amplitude as a possible training stimulus.

Investigation of Inter-Limb Symmetry in Knee Extensors Using Different Strength Outcome Measures

Muscle performance between contra-lateral knee extensors is most often assessed using maximal test for isometric/isokinetic torque evaluation. Recently, the rate of force development scaling factor (RFD-SF) has been used to evaluate neuromuscular capacity with a range of submaximal target peak torques, which could highlight other aspects of inter-limb (a)symmetry. The aim of our study was to investigate the differences, associations, and agreement between inter-limb symmetries of knee extensors using maximal torque (T_max) rate of torque development (RTD), slope of the RFD-SF regression line (k), and theoretical peak of RTD (TP_RTD). A total of 236 young, healthy athletes participated in the cross-sectional study. All participants performed unilateral knee extension (maximal voluntary contraction protocol and RFD-SF protocol) with both legs in the isometric knee dynamometer. Inter-limb symmetries were calculated for each outcome measure. Our results showed significant differences between all symmetry values (T_max (91.7%), RTD (85.2%), k (94.2%), TP_RTD (95.9%)). Significant strong correlations were found between symmetry values calculated from k and TP_RTD (r = 0.88, p < 0.001), while weak correlation was found between T_max and RTD (r = 0.17, p < 0.01. Fair agreement regarding leg dominance was found between T_max and RTD values. Our results suggest that inter-limb (a)symmetries are metric- and task-specific.

Should We Use Unilateral or Bilateral Tasks to Assess Maximal and Explosive Knee Extensor Strength in Patients with Knee Osteoarthritis? A Cross-Sectional Study

Deficits in maximal and explosive knee extensor strength, which are usually assessed with unilateral tasks, are substantial in patients with knee osteoarthritis (KOA). The aim of this study was to investigate the clinical relevance of unilateral vs. bilateral tasks for assessing knee extensor strength in patients with KOA. This was achieved primarily by comparing unilateral and bilateral inter-limb strength asymmetries and secondarily by examining the relationship between unilaterally and bilaterally measured strength, and performance-based and self-reported function. Twenty-four patients with unilateral KOA (mean age: 65 ± 7 years) performed isometric gradual and explosive maximal voluntary contractions to assess, respectively their maximal and explosive strength. Performance-based and self-reported function were also evaluated with standard functional tests and questionnaires, respectively. Inter-limb asymmetries of maximal and explosive strength did not differ significantly between unilateral (mean asymmetry: 26 ± 15%) and bilateral tasks (22 ± 21%). In the same way, the relationships between knee extensor strength-measured either unilaterally or bilaterally-and performance-based or self-reported function were not influenced by the type of task. In conclusion, it does not seem to make a difference in terms of clinical relevance whether maximal and explosive knee extensor strength are evaluated with unilateral or bilateral tasks in KOA patients.

Comparison between gymnasts and non-gymnasts in isometric strength of the lower limbs

Muscle asymmetries in gymnasts are common and can lead to injury. We aimed to determine differences in hip, knee, and ankle strength between female gymnasts and non-gymnasts, and secondly, to determine the effect of strength training intervention. Fifteen gymnasts (aged 11.19 ± 1.89 years) and 15 non-gymnasts (aged 10.92 ± 1.96 years) performed unilateral isometric maximal voluntary contractions of the hip (extensor, flexor, abductor, adductor, internal and external rotator), knee and ankle flexors and extensors on a dynamometer. Inter-limb asymmetries (ILAs) were compared across strength outcomes (MVC torque) and groups. ILAs was calculated based on the strength measurements. The gymnasts were retested after 8 weeks, during which the participants performed 5 weeks of regular training and 3 weeks of targeted strength training intervention. We found significant differences between groups in most observed hip strength parameters, but not in knee and ankle strength. The intervention did not significantly affect any parameter of ILAs. Gymnasts and non-gymnasts differ in hip strength parameters. A longer intervention program may decrease ILA parameters.

Maximal Isometric or Eccentric Hamstring Strength-Which Test Modality Might Be More Suitable for Assessments in Youth Alpine Ski Racers?

Background: Physical fitness is an important component in the development of youth alpine ski racers. To write systematically planned and age-appropriate fitness programs athletes need to be physically tested at regular intervals at an early age. Although well-developed hamstring muscle strength is important for alpine ski racing performance and the prevention of serious knee injuries, it has not been well investigated, especially in youth athletes. Accordingly, the first aim of the present study was to assess the test-retest reliability of the maximum bilateral eccentric (MBEHS) and unilateral isometric (MUIHS) hamstring tests. The second aim of the present study was to assess whether the results of these two methods correlate and if it is possible to commit to one of the two methods to provide an economic test procedure. Methods: The first study included 26 (14 females/12 males) youth alpine ski racers aged between 12 and 13 years. All athletes performed two MBEHS and two MUIHS tests, 7 days apart. The intraclass correlation coefficient (ICC 3,1) and their 95% confidence intervals based on a consistency two-way mixed model were used to estimate the reliability of the two different test modalities. The second study included 61 (27 females/34 males) youth alpine ski racers aged between 10 and 13 years. All athletes performed one MBEHS and one MUIHS test. Bland-Altman plots and the 95% limits of agreement as well as correlations by Pearson (r) between the different test modalities were assessed. Results: In study 1 “poor” to “moderate” (MBEHS right leg 0.79 (0.58–0.90); left leg 0.83 (0.66–0.92); MUIHS right leg 0.78 (0.56–0.89); left leg 0.66 (0.37–0.83)) ICC values and 95% confident intervals were obtained. Standard error of measurement (SEM) between trails was between 18.3 and 25.1 N. Smallest detectable difference (SDD) was between 50.8 and 69.5 N. In study 2 mean differences between MBEHS and MUIHS was around 20 N with higher values for MBEHS. Significant moderate-to-strong correlations were found between the test modalities (r = 0.74–0.84, p <0.001). Conclusions: The MBEHS test has higher ICC values, lower CV values, higher SEM values and lower SDD values than the MUIHS test. All this suggests that the MBEHS test is more suitable than the MUIHS test to determine the maximum hamstring force in young alpine ski racers.

Portable fixed dynamometry: towards remote muscle strength measurements in patients with motor neuron disease

Background

We aimed to determine (1) the test–retest reliability of a newly developed portable fixed dynamometer (PFD) as compared to the hand-held dynamometer (HHD) in patients with motor neuron disease (MND) and (2) the PFD’s ability to reduce possible examiner-induced ceiling effects.

Methods

Test–retest reliability of isometric muscle strength of the quadriceps was measured in patients with MND and non-neurological controls using the HHD and PFD. Reliability was estimated by the intraclass correlation coefficient (ICC) and standard error of measurement (SEM) using linear mixed effects models, and the Bland–Altman method of agreement.

Results

In total, 45 patients with MND and 43 healthy controls were enrolled in this study. The ICC of the PFD was excellent and similar in both patients and controls (ICC _Patients 99.5% vs. ICC _Controls 98.6%) with a SEM of 6.2%. A strong examiner-induced ceiling effect in HHD was found when the participant’s strength exceeded that of examiner. Employing the PFD increased the range of muscle strength measurements across individuals nearly twofold from 414 to 783 N.

Conclusions

Portable fixed dynamometry may significantly reduce examiner-induced ceiling effects, optimize the standardization of muscle strength testing, and maximize reliability. Ultimately, PFD may improve the delivery of care due to its potential for unsupervised, home-based assessments and reduce the burden to the patient of participating in clinical trials for MND or other neuromuscular diseases.

Reference Values for Isometric, Dynamic, and Asymmetry Leg Extension Strength in Patients with Multiple Sclerosis

Having recognized the value of resistance training in patients with multiple sclerosis (PwMS), there are a lack of lower limb normative reference values for one repetition maximum (1RM) and maximal voluntary isometric contraction (MVIC) in this population. Hence, the purposes of this study were to provide reference values for 1RM and MVIC of knee extensors in PwMS across the disability spectrum and to examine knee extension strength asymmetry. Three hundred and ninety PwMS participated in the study, performing MVIC and 1RM tests of bilateral (both legs together at once) and unilateral (each leg singly) knee extensors. There was no difference in 1RM according to the disease course of MS, but there was according to the degree of neurological disability, being more preserved in those with a lower degree of disability. MVIC tends to be higher in patients with relapsing-remitting MS respect those with progressive MS, and in patients with lower levels of neurological disability. Asymmetry above the values considered normal in 1RM was present in 20-60% of patients and 56-79% in the MVIC test, depending on the type of MS and tended to be lower in those with less disability. Reference values are given by quartiles for 1RM, MVIC, and asymmetry.

Change of Direction Performance Is Influenced by Asymmetries in Jumping Ability and Hip and Trunk Strength in Elite Basketball Players

Change of direction (COD) ability is essential for sport performance in high level team sports such as basketball, however, the influence of asymmetries on COD ability is relatively unknown. Forty-three junior and senior level elite basketball players performed isometric hip and trunk strength testing, passive hip and trunk range of motion testing, and unilateral horizontal and vertical jumps, as well as the T-test to measure COD performance. Mean asymmetry values ranged from 0.76% for functional leg length up to 40.35% for rate of torque development during hip flexion. A six-variable regression model explained 48% (R2 = 0.48; p < 0.001) of variation in COD performance. The model included left hip internal/external rotation strength ratio, and inter-limb asymmetries in hip abduction rate of torque development, hip flexion range of motion, functional leg length, single leg triple jump distance, and peak torque during trunk lateral flexion. Results suggest that the magnitude of asymmetries is dependent of task and parameter, and using universal asymmetry thresholds, such as <10 %, is not optimal. The regression model showed the relationship between asymmetries and COD performance. None of tests were sufficient to explain a complex variable like COD performance.