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Problem statement: Bilateral assessment of knee strength is crucial for identifying and understanding lower limb strength asymmetry. However, there is a scarcity of data in the literature regarding the bilateral strength asymmetry of knee extensors in healthy, untrained individuals, particularly in relation to a limited number of tested positions. Aims: 1) To investigate and quantify the bilateral knee extensor strength asymmetry between the dominant (DL) and non-dominant leg (NDL) in nonathletes. 2) To utilize dynamometric measurements to assess isometric peak torque (PT) across the full range of motion. 3) To apply an optimal mathematical function for modelling the torque-angle relationship, allowing a detailed examination of the respective curves for both legs using the bilateral asymmetry index (BAI). Methods: Isometric peak torque (PT) was measured using isokinetic dynamometry (Biodex 4Pro) in a cohort of 12 male nonathletes (age of 26 ± 7 years, height of 1.8 ± 0.1 m, and body mass of 78 ± 10 kg). Measurements were taken at various positions (°): 20, 40, 60, 70, 80, 90, 100, and 110. The data were modelled with rational function, established to be the optimal and the obtained torque-angle curves were grouped in three asymmetry patterns, based on the BAI values and the behaviour of the DL and NDL curves. The physical activity of nonathletes was evaluated as a sum of points for current weekly exercise and for sport training in the childhood-adolescent age. Results: The first pattern presents low levels of bilateral asymmetry (with BAI<15%) in the whole range of motion. The second one demonstrate high asymmetry in the angular range 80°-110° (BAI up to 27%), while in the third pattern, asymmetry was observed in both ranges: 20°-40° (BAI between 28 -31%) and 90°-110° (BAI up to 26.4% and 39.7%in the range of optimal or close to optimal muscle length). Particular for the third pattern was: - a rightward shift of the maximal PT in the knee joint torque-angle curve only in the DL; - a stronger NDL in the range where extensors are shorter; and - a highest score for the level of physical activity. Conclusions: These results pointed out that leg dominance appears to form different motor skills of knee extensors, which can result in strength asymmetry variations in nonathletes. Therefore, we recommend paying attention to knee extensors strength diagnostics in nonathletes. Thus, based on the results from this research, we suggest a minimum of two knee positions for bilateral asymmetry evaluation in healthy men, one of which at shortened extensors in the range 30-50° and one at lengthened in the range 80-90°. [ABSTRACT FROM AUTHOR]

Background: The ability to maintain a submaximal force as a muscle fatigues is supplemented by compensatory adjustments in the nervous system's control of motor units. Aim: We sought to compare vastus lateralis motor unit recruitment and firing rate data for younger versus older men during isometric fatigue. Methods: Twelve younger (age = 25 ± 3 years) and 12 older (75 ± 8 years) men performed contractions of the knee extensors at 50% of maximal voluntary contraction force until exhaustion. Surface electromyographic (sEMG) signals were detected from the vastus lateralis. A sEMG signal decomposition algorithm was used to quantify the motor unit action potential (MUAP) amplitude, mean firing rates, and recruitment threshold of each motor unit. For the latter two variables, our analyses only included motor units that featured similar action potential amplitude throughout the protocol. Results: There was no group difference for time to task failure (p = 0.362, d = 0.381). Both groups showed increases in MUAP amplitude [younger and older slopes = 0.0174 ± 0.0123 and 0.0073 ± 0.0123 mV/contraction, respectively (p = 0.082, d = 0.710)], but the change was more linear for the younger men (mean r2 values = 0.565 and 0.455). Mean firing rates increased over time for the younger (p < 0.001), but not the older (p = 0.579), men. Similarly, recruitment thresholds decreased for younger men (p = 0.001). Conclusion: We propose that aging results in neuromuscular impairments that hinder older adults' ability to make compensatory adjustments in motor unit control during fatigue. [ABSTRACT FROM AUTHOR]

Finswimming is a sport where athlete uses one big monofin to produce propulsion. The purpose of this study was to describe relationship between isokinetic strength of different muscle groups and 100 meters finswimming time. Study questions was: what muscle groups have relationship with finswimming time. Methods: 17 international level monfin swimmers, 9 male (age 16,9 ±1,8 yrs., height 180,0 ± 10.0 cm., weight 76.0±6.9 kg) and 8 female finswimmers ( age 17,6 ±4,7 yrs., height 170,0 ± 10.0 cm., weight 68,6 ± 13,5 kg) performed 100 meters monofin surface swim and where also tested within a two days on isokinetic dynamometer (knee, hip and trunk extensors and flexors at angular speeds of 60°/sec ). Force data at angles from 0-90 degrees with 10 degree step were used for correlation. Results: There was a strong correlation (p<0.05) between swimming time and knee extensors (r=-0.82 at angle 50°), hip flexors (r=-0.70 at angle 10°) and trunk flexors (r =-0.77 at angle 20°) in male swimmers. Surprisingly, we did not find corresponding correlations among female finswimmers. Conclusion: Current study found relationship between strength of main muscle groups and swimming speed only in male swimmers. It is expected that strength plays a role in swimming time, but the lack of relationship in female swimmers suggests at the need to introduce a measure of swimming effectiveness instead of pure resultant time. The proposed hypothesis is further supported by the high level of competence among study participants (incl. multiple European champion, and several finalists). [ABSTRACT FROM AUTHOR]

PURPOSE/BACKGROUND: Patients after total knee arthroplasty (TKA) are known to exhibit deficits in quadriceps muscle activation. The purpose of this study was to determine if quadriceps activation levels in patients after TKA at the beginning of rehabilitation would influence quadriceps strength after rehabilitation. DESIGN: A secondary analysis of data from a prospective, randomized, longitudinal clinical trial. SETTING: Institutional clinic and research laboratory. PARTICIPANTS: Patients who underwent unilateral TKA (Men= 102; Female= 84). MAIN OUTCOME: Voluntary activation of the quadriceps during maximal voluntary isometric contractions (MVIC) was measured using the central activation ratio (CAR). Hierarchical multivariate regression analysis was used to determine if CAR prior to treatment could predict MVIC after the strength training intervention. RESULTS: After controlling for age, sex, and initial strength levels (R(2)= 0.548; p<0.001), the predictability of quadriceps strength after the 6-week intervention did not change when pain during MVIC (R(2)= 0.551; p= 0.317) and pre-rehabilitation activation levels (R(2)= 0.551; p= 0.818) were introduced into the regression. CONCLUSIONS: Initial quadriceps activation levels, for patients who underwent TKA, did not predict the quadriceps strength following a strength training intervention. Therefore, deficits in voluntarily activation post-operatively should not be considered as a rate-limiting factor in recovering quadriceps strength after TKA. LEVEL OF EVIDENCE: Retrospective cohort study. Level IIb. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine the differences in knee extensor maximal and endurance strength in elderly. Sixteen healthy elderly served as subjects, eight of them trained , age 61.0±8.9 yrs; height, 170.6±6.8 cm; weight, 71.8±11.7 kg [mean ± standard deviation] and eight untrained 61.4±8.1 yrs, height 174.6±7.4 cm; weight 83.9 ±14.2 kg. Maximal strength in single leg extension exercise was measured unilaterally with the dominant leg until the subjects reached their 1 Repetition Maximum (RM) covering the full Range of Motion (ROM). Muscular endurance was obtained with a load of 75% of 1-RM for 3 consecutive sets, with 2 min rest periods till failure. Load at 1 RM was lower in absolute terms in untrained, but not significant, while the relative 1-RM test was significantly lower in untrained subjects (0.20 vs. 0.25 kg load/kg body weight) (p< 0.05). The number of repetitions and amount of weight lifted performed of all 3 sets was higher in trained subjects, but not significant. In the trained group both repetitions and the load managed in the third set was significant lower compared with the first two sets. The result that maximal force output is more affected compared to muscular endurance in these subjects might be due to the habitual use of quadriceps femoris muscles during activity of daily living in both trained and untrained elderly. [ABSTRACT FROM AUTHOR]

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This study assessed the relationship between isokinetic leg strength and 10 to 30-m sprint times in 14 professional English Premier League football players: 6 international and 8 non-international. Isokinetic measurements were performed at 60, 180, 240 and 300°-s-1 on knee extensors and flexors. International players were shorter (179 ± 7 cm versus 185 ± 2.5 cm, P < 0.01), lighter (78.6 ± 4.8 kg versus 88.8 ± 6 kg, P < 0.01) and leaner (11.4 ± 1% versus 14.3 ± 2.2%, P < 0.02) than the non-international players. In absolute values, extensor peak torques (PT) were significantly lower for the international players than for the non-international players at 60, 180, 240 and 300°-s-1 while flexor PT were significantly lower only at 180, 240 and 300°-s-1. These differences were explained by body weight variations. Indeed, when expressed per kg of body weight no differences for both extensor and flexor PT were found between national and international football players. There were no differences in the sprint times either. In the whole population, extensor peak torques were related to the 20-30-m sprint performance at 180, 240 and 300°-s-1 (r = 0.77, r = 0.74, and r = 0.80, P < 0.01, respectively). High muscle strength was needed for 30-m sprint times. However, international football players were not stronger than national players, highlighting the major importance of both well-developed tactical sense and high technical standard. [ABSTRACT FROM AUTHOR]