Single-joint isometric and isokinetic knee strength assessment plays an important role in strength and conditioning, physical therapy, and rehabilitation. The literature, however, lacks absolute ...reference values. We systematically reviewed the available studies that assessed isometric knee strength. Two scientific databases (PubMed and PEDro) were searched for the papers that are published from the inception of the field to the end of 2019. We included studies that involved participants of both genders and different age groups, regardless of the study design, that involved isometric knee extension and/or flexion measurement. The extracted data were converted to body-mass-normalized values. Moreover, the data were grouped according to the knee angle condition (extended, mid-range, and flexed). A meta-analysis was performed on 13,893 participants from 411 studies. In adult healthy males, the pooled 95% confidence intervals (CI) for knee extension were 1.34–2.23Nm/kg for extended knee angle, 2.92–3.45Nm/kg for mid-range knee angle, and 2.50–3.06Nm/kg for flexed knee angle, while the CIs for flexion were 0.85–1.20, 1.15–1.62, and 0.96–1.54Nm/kg, respectively. Adult females consistently showed lower strength than adult male subgroups (e.g., the CIs for knee extension were 1.01–1.50, 2.08–2.74, and 2.04–2.71Nm/kg for extended, mid-range, and flexed knee angle condition). Older adults consistently showed lower values than adults (e.g., pooled CIs for mid-range knee angle were 1.74–2.16Nm/kg (male) and 1.40–1.64Nm/kg (female) for extension, and 0.69–0.89Nm/kg (male) and 0.46–0.81Nm/kg (female) for flexion). Reliable normative for athletes could not be calculated due to limited number of studies for individual sports.
Aim:
Sufficient strength and dynamic stability of the lower limbs are essential for improving punching force and preventing injury in amateur boxers. However, there are still no comprehensive reports ...on the isokinetic knee strength of boxers with different performance levels. The current study aimed to profile the isokinetic muscle strength of flexion and extension of the knee in boxers, as well as bilateral, unilateral, and functional ratios, and investigate the variation in these muscle strength characteristics associated with different performance levels.
Methods:
Boxers were divided in two performance groups, elite (five males and four females) and non-elite groups (five males and four females). Muscle strength of the knee was determined
via
an IsoMed2000 device. Parameters examined included peak torque of the hamstring (H) and quadriceps (Q) during concentric (con) and eccentric (ecc) contractions at low (60°/S), medium (180°/S), and high (240°/S) speed and bilateral ratios (BLs), unilateral ratios (ULs), and functional ratios of dominant (D) and non-dominant limbs.
Results:
In all angular velocities, the peak torque of H and Q was stronger in the elite group than in the non-elite group. ULs were lower in the elite group than in the non-elite group in Hcon/Qcon at 180D (
p
< 0.01) and 180ND (
p
< 0.05) and in Hecc/Qecc at 60D, 180D (
p
< 0.05) and 240D (
p
< 0.01). The elite group had higher BLs than the non-elite group in Hcon at 60°/S (
p
< 0.05) and Qcon at 180°/S (
p
< 0.05). The non-elite group had a higher functional ratio than elite boxers in Hecc/Qcon at 180D and 240D (
p
< 0.01).
Conclusion:
Elite boxers had stronger knee strength in con and ecc contractions. All boxers had normal Hecc/Qecc and Hcon/Qecc. Hcon/Qcon and Hecc/Qcon were abnormal at lower angular velocity. Elite boxers had higher BLs and lower ULs, indicating that they are at a higher risk of injury.
Administration of testosterone (T) is associated with increased serum T concentrations and improved physical performance in women. However, the inter-individual variation in T concentrations after T ...treatment is large and may in part be due to genetic variations. Serum T, as well as dihydrotestosterone (DHT), androstenedione (A) and the T/A ratio have been suggested as promising doping biomarkers for testosterone intake. Here, polymorphisms in androgen metabolic enzyme genes have been investigated in healthy women prior to and after 10 weeks administration of testosterone cream. Klotho is a protein that has been associated with anaerobic strength and here a genetic variation in klotho gene was studied in relation to performance as measured by isokinetic knee strength, as well as to serum androgen disposition. The AKR1C3 genotype (rs12529) was associated with serum T levels at baseline, whereas serum concentrations post T treatment did not differ between genotypes. The SLCO2B1 (rs12422149) and UGT2B17 deletion polymorphisms were not associated with serum concentration of either T, DHT or A. The klotho polymorphism (rs9536314) was associated with serum concentrations of both total T and T/A ratio after T administration. Individuals with the GT genotype increased T concentrations and T/A ratio more than women homozygous for the T allele. No significant difference in the association of klotho genotype with knee muscle strength was observed between placebo and T treatment. However, individuals homozygous for the T allele showed higher isometric mean torque scores at exit than GT subjects after T administration. This is the first time a genotype has been associated with androgen concentrations after T administration and muscle strength in women. Our results imply that subjects with a polymorphism in klotho may be more prone to detection using serum T and A as biomarkers.
The purpose of the study was to compare physical characteristics and performance values between different playing positions in professional female team handball. Twenty-nine female handball players ...were categorized as centers (n=6), pivots (n=9), wings (n=8) or goalkeepers (n=16). Measurement of physical characteristics including body height and mass, body mass index; knee muscle strength, scores on the lower limb vertical power (vPower), lower and upper limb performance and trunk extension endurance were determined and compared across playing positions. The goalkeepers had higher knee strength as compared to pivots, wings, and centers (p<.001, ηp2>.20). Pivot players achieved higher vPower than wings, centers, and goalkeepers (p=.011, ηp2=.759). In addition, goalkeepers and wings achieved higher vPower than centers (p<.001, ηp2=.759). No significant differences were observed in trunk extension endurance and upper limb performance results according to playing positions (p>.05, ηp2<.20). The pivots and wings had better lower limb performance than goalkeepers and centers (p<.001, ηp2=.682-.701). The present study concludes that depending on their play positions, there are differences in terms of physical characteristics, knee muscle strength, vertical power, and lower extremity performance in elite female handball players. These results could help improve coaches' knowledge of elite female teams in the particular in the country where the study was conducted and in others of similar characteristics.
Individuals with autism spectrum disorder (ASD) often exhibit motor deficits that increase their risk of falls. There is a lack of understanding regarding gait biomechanics demonstrated by older ...children with ASD. The purpose of the study was to determine differences in gait patterns between older children with ASD and typically developing children. Eleven children with ASD and 11 age- and gender-matched typically developing children were recruited for the study. Participants walked on a force-instrumented treadmill at a constant speed (1.1 m/s - 1.2 m/s) for five minutes (min). Participants performed maximal voluntary contractions to assess their knee muscular strength. Differences between individuals with ASD and matched control participants were examined through paired t-tests with a significance level of p ≤ 0.05. Individuals with ASD demonstrated a smaller knee extensor torque compared to controls (p = 0.002). Participants with ASD exhibited a shorter stride length (p = 0.04), a greater cadence (p = 0.03), and a higher variation in stride width (p = 0.04) compared to control participants. The individuals with ASD experienced a greater braking ground reaction force (p = 0.03) during loading response. The results indicate older children with ASD develop a unique gait pattern signified by a reduced stride length, increased cadence, and an increase of variation in stride width. This unique gait pattern may represent a movement strategy used by the individuals with ASD to compensate for the weakness associated with their knee extensor muscles. Individuals with ASD who demonstrate these unique gait deviations may face reduced postural stability and an increased risk of fall-related injuries.
Bilateral symmetry evaluation in lower limb is used for injury prevention, and is an indicator of returning to post-injury activity. The aim of present study was to investigate the effect of ...different angular velocities on asymmetry of the hamstring-to-quadriceps strength ratio.
Isokinetic concentric hamstring to quadriceps (H:Q) peak torque ratio of the 27 male and female professional basketball players was measured at seven angular velocities (60, 90, 120, 150, 180, 180, 240, 300 deg s−1) on both dominant and non-dominant legs with Biodex Isokinetic Dynamometer. Repeated measure analysis of variance was used to assess the effects of angular velocity and limb side on our outcomes (p≤ 0.05).
The results showed that with increasing angular velocity, the ratio of hamstrings to quadriceps increases (p = 0.001). There was no difference between dominant and non-dominant limbs in the H:Q peak torque ratio (p = 0.254). In addition, velocity of measurement did not affect the bilateral asymmetry of peak torque ratio of the H:Q of both sides (p = 0.852).
Based on the results of this study, it can be concluded that measurement velocity does not affect the bilateral asymmetry of the H:Q peak torque ratio of the dominant and non-dominant limbs. In clinical assessments of H:Q bilateral asymmetry, we suggest that physical trainer can assess bilateral asymmetry of H:Q with arbitrary angular velocities.
This study aimed to develop alternative prediction equations to predict isokinetic muscle strength at 60°/s based on anthropometric characteristics, including body mass, height, age, and sex for ...young and middle-aged non-athlete populations.
Three hundred and thirty-two healthy non-athletic participants (174 females, 158 males) between 20 and 59 years underwent a 60°/s isokinetic knee joint concentric contraction test. Forty people were randomly selected for retesting to assess the reliability of the isokinetic instrument. Multivariate linear regression was used to establish extension peak torque (EPT) and flexion peak torque (FPT) prediction equations. Sixty extra participants were used individually to validate the prediction equations, and Bland Altman plots were constructed to assess the agreement of predicted values with actual measurements.
The result demonstrated that the instrument we used has excellent reliability. The multivariable linear regression model showed that body mass, age, and sex were significant predictors of PT (EPT: Adjusted R
= 0.804, p < 0.001; FPT: Adjusted R
= 0.705, p < 0.001). Furthermore, the equations we established had higher prediction accuracy than those of Gross et al. and Harbo et al. CONCLUSION: The equations developed in this study provided relatively low bias, thus providing a more suitable reference value for the knee isokinetic strength of young and middle-aged non-athletes.
Familiarization is necessary for an accurate strength assessment as it reduces confounding factors such as learning and training effects. However, the number of contractions required for ...familiarization and whether cross-limb transfer during familiarization could affect bilateral assessment are unknown. This study aimed at identifying the number of maximum contractions required for isokinetic knee extension and flexion familiarization in both dominant (D) and non-dominant limb (ND).
Twenty-eight right-limb dominant males (age: 22.64 ± 2.60 years, BMI: 23.82 ± 2.85 kg/m2) performed a total of 6 sets (each consisted of 5 continuous maximum contractions) at 60o/s for each limb.
The number of sets required for familiarization is determined when the average peak torque achieved stabilization from the series of contractions of each limb. For knee extension, 3 sets (15 contractions) were required for familiarization, whereas 2 sets (10 contractions) for knee flexion in both limbs. Interestingly, for knee extension in ND, the number of sets required for familiarization was reduced to 2 following contralateral contractions in D, however, for knee extension in D, there was no difference in the number of sets required for familiarization following contralateral contractions in ND. While for knee flexion, no cross-limb transfer was observed. These observations suggest the presence of cross-limb transfer from D to ND during familiarization which implies the involvement of the central nervous system.
Practically, familiarization for bilateral isokinetic strength assessment for knee extension and flexion at 60o/s should begin with the dominant limb for 3 sets to obtain accurate and reliable measurements.
Background:
Return-to-sports (RTS) rates after anterior cruciate ligament (ACL) reconstruction (ACLR) differ according to the level at which patients return. It is unclear whether the level of RTS is ...affected by psychological readiness to return.
Purpose:
To examine the association between psychological readiness to RTS and subjective RTS level 12 months after ACLR.
Study Design:
Case-control study; Level of evidence, 3.
Methods:
A total of 47 patients who underwent unilateral primary ACLR surgery were enrolled. Assessments at 6 and 12 months postoperatively consisted of knee strength testing (isokinetic quadriceps and hamstring strength), the International Knee Documentation Committee Subjective Knee Evaluation Form (IKDC-SKF), and the Anterior Cruciate Ligament-Return to Sport after Injury (ACL-RSI) scale to measure psychological readiness to RTS. Patients were assigned to 1 of 3 subgroups based on their subjective assessment of RTS level at 12 months postoperatively: RTS at or above preinjury level (RTS≥Pre; n = 19), RTS below preinjury level (RTS<Pre; n = 24), or no RTS (n = 4). Two-way mixed-model analysis of variance was used to examine the effects of RTS subgroup, postoperative time point, and group × time interaction with patient characteristics, knee strength, and IKDC-SKF and ACL-RSI scores. Multivariate logistic regression analysis was performed to determine which factors were associated with RTS subgroupings.
Results:
Significant differences were found among the RTS≥Pre, RTS<Pre, and no-RTS groups in age, ACL-RSI score at 6 and 12 months, quadriceps strength at 6 and 12 months, and IKDC-SKF score at 6 and 12 months (P < .001 for all). Multivariate logistic regression analysis revealed that RTS at or above preinjury level was associated with higher ACL-RSI score at 12 months postoperatively (odds ratio OR, 1.11; 95% CI, 1.05-1.20; P = .003) and younger age (OR, 0.80; 95% CI, 0.61-0.92; P = .012).
Conclusion:
The ACL-RSI score was significantly different among the study groups, and the ACL-RSI score at 12 months postoperatively and younger age were associated with RTS at or above preinjury level.
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