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Time‐of‐Day Effect on the Torque and Neuromuscular Properties of Dominant and Non‐Dominant Quadriceps Femoris
Abstract
The study was conducted first, to determine the possibility of a dichotomy between circadian rhythm of maximal torque production of the knee extensors of the dominant and non-dominant legs, and second, to determine whether the possible dichotomy could be linked to a change in the downward drive of the central nervous system and/or to phenomena prevailing at the muscular level. The dominant leg was defined as the one with which subjects spontaneously kick a football. Tests were performed at 06:00, 10:00, 14:00, 18:00, and 22:00 h. To distinguish the neural and muscular mechanisms that influence muscle strength, the electromyographic and mechanical muscle responses associated with electrically evoked and/or voluntary contractions of the human quadriceps and semi-tendinosus muscles for each leg were recorded and compared. The main finding was an absence of interaction between time-of-day and dominance effects on the torque associated with maximal voluntary contraction (MVC) of both quadriceps. A significant time-of-day effect on MVC torque of the knee extensors was observed for the dominant and non-dominant legs when the data were collapsed, with highest values occurring at 18:00 h (p < 0.01). From cosinor analysis, a circadian rhythm was documented (p < 0.001) with the peak (acrophase) estimated at 18:18 +/- 00:12 h and amplitude (one-half the peak-to-trough variation) of 3.3 +/- 1.1%. Independent of the leg tested, peripheral mechanisms demonstrated a significant time-of-day effect (p < 0.05) on the peak-torque of the single and doublet stimulations, with maximal levels attained at 18:00 h. The central activation of the quadriceps muscle of each leg remained unchanged during the day. The present results confirmed previous observations that muscle torque changes in a predictable manner during the 24 h period, and that the changes are linked to modifications prevailing at the muscular, rather than the neural, level. The similar rhythmicity observed in this study between the dominant and non-dominant legs provides evidence that it is not essential to test both legs when simple motor tasks are investigated as a function of the time of day.
... These circadian rhythms exist in virtually every physiological measure of performance and are controlled by a 'brain clock' located in the suprachiasmatic nucleus of the hypothalamus (Bailey & Silver, 2014;Douglas et al., 2021;Kuljis et al., 2013). Time-dependent variations in maximal performance during waking hours have been documented in laboratory settings (Gauthier et al., 1996;Guette et al., 2005a;Sedliak et al., 2008) and competitive sports events (Lok et al., 2020). Evidence exists for alterations in neural excitation (Gueldich et al., 2016;Lang et al., 2011;Martin et al., 1999), neurohormonal flux (Chtourou et al., 2012;Racinais et al., 2005;Tamm et al., 2009), contractile alterations at the muscle fiber level (Mirizio et al., 2020;Sedliak et al., 2008), and some recent hypotheses implicate circadian clock genes (Douglas et al., 2021;Dyar et al. 2012). ...
... The influence of time of day on maximal isometric force has been documented across many muscle groups (Drust et al., 2005;Gauthier et al., 1996;Küüsmaa et al., 2016). There is some evidence (Guette et al., 2005a;2005b, Knaier et al., 2019) that different muscle groups may respond uniquely in the morning versus evening, yet direct comparisons between limbs are lacking. Since the muscles of the lower limb are involved in locomotor activity throughout the day, it may be that ambulation provides a passive warmup effect not shared by the muscles of the upper limb. ...
... An a priori power analysis was performed based on the effect sizes of morning versus evening isometric forces for the elbow flexors (Gauthier et al., 1996;Guette et al., 2005a) and knee extensors (Giacomoni et al., 2005). The power analysis was performed as described by Beck (2013) for a within-between interaction with α set at 0.05, power set at 0.80, two groups, two measurements, and an effect size of (0.30). ...
The time‐of‐day influence on neuromuscular function is well‐documented, but important details remain elusive. It is currently unknown whether males and females differ in their diurnal variation for optimal neuromuscular performance. The purpose of this study is to identify the time‐of‐day influence on neuromuscular function between sexes and determine whether these responses differ for the upper versus lower limbs. A group of males (n = 12) and females (n = 15) completed neuromuscular performance testing in the morning (07:00–09:00) and evening (17:00–19:00) on separate days in a randomized order. Maximal force, the normalized rate of force development, EMG, normalized EMG rise, and submaximal force steadiness were compared between morning and evening hours. The main findings show that maximal force was greater in the evening for the knee extensors (d = 0.570, p < 0.01) but not the elbow flexors (d = 0.212, p = 0.281), whereas maximal muscle excitation was greater in the evening for the biceps brachii (d = 0.348, p < 0.01) but not the vastus lateralis (d = 0.075, p = 0.526) with no influence of sex. However, force steadiness during knee extension was superior in the evening versus the morning for males (d = 0.734, p = 0.025) and compared to evening values for females (g = 1.19, p = 0.032). Overall, these findings show that time‐of‐day affects the knee extensors more than the elbow flexors and that diurnal variability between sexes appears to be task‐dependent.
... Rahnama et al. [4] (2006) observed electromyography activity of selected lower limb muscle fatigue by exercise at the intensity of soccer match play. Guette et al. [5] (2005) studied neuromuscular properties of dominant and non-dominant quadriceps of femoris and the torque. ...
Content: Electromyography (EMG) is a recording of muscles electrical activity and is useful for mechanism study. In Exercise and Sport Science, mechanism of dominance and non-dominance limb activity is recently a focus area. Objective: The aim of this study is to observe the muscle electrical activity of soccer players' dominant and non-dominant leg. Design: Cross-sectional study. Setting: District level soccer championship, Birbhum district, West Bengal, India. Patients or Other participants: The total of 10 subjects, 5 right foot dominated and 5 left foot dominated soccer players were selected. Main outcome measure(s): Muscle electrical activity was measured by Electromyography (EMG) machine and data were collected during resting standing position from the leg muscles (calf, quadriceps and hamstring). Bipolar, 5 mm diameter surface electrodes were used to collect the data. Each group of muscle electrical activity was recorded after 15 seconds for 5 minutes. Two minutes rest intervals were given between three trials. For analysis of the data mean, SD and independent t-test was used. Results: It was observe that in the right leg dominant players and left leg dominant players EMG activity of calf and quadriceps muscles were significantly higher in their dominant leg. Whereas in the hamstring muscle EMG activity of left leg dominant players was significantly higher in their left leg, and insignificant result was found in the right leg dominant players. Conclusion: The present research group concluded that dominant leg of soccer players has shown higher level of EMG activity in the resting standing position. This result may create an impact in the mechanism study of dominance limb.
... In studies where aspects related to nutrition timing/intake are not mentioned at all, could potentially mask or increase morning-evening difference in many physiological variables (Bougard et al. 2009). All studies did report information related to participant background and fitness levels, thus unlikely negatively influencing findings (Guette et al. 2005;Häkkinen 1989). Nevertheless, training status (trained vs. untrained) does influence performance in different modalities (Bishop and Spencer 2004;Hopker et al. 2013;Riboli et al. 2021). ...
Few functional measures related to time-trial display diurnal variation. The diversity of tests/protocols used to assess time-trial performance on diurnal effects and the lack of a standardised approach hinder agreement in the literature. Therefore, the aims of the present study were to investigate and systematically review the evidence relating to time-of-day differences in time-trial measures and to examine the main aspects related to research design important for studies of a chronobiological nature. The entire content of Manipal Academy of Higher Education electronic library and Qatar National Library, and electronic databases: PubMed (MEDLINE), Scopus and Web of Science were searched. Research studies published in peer-reviewed journals and non-peer reviewed studies, conducted in male adult participants aged ≥18 y before November 2021 were screened/included. Studies assessing tests related to time-trials in any modality between a minimum of 2 time-points during the day (morning [06:30-10:30 h] vs evening [14:30-20:00 h]) were deemed eligible. The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) process was used to assess the evidence to inform recommendations. The primary search revealed that a total of 10 from 40 articles were considered eligible and subsequently included. Six were conducted using cycling, two using running and two using swimming as the mode of exercise. Distances ranged from 1 to 16.1-km in distance or 15 to 20-min time in the cycling and running time-trials, and 50 to 200-m in the swimming time-trials. Only four studies found one or several of their performance variables to display daily variations, with significantly better values in the evening; while six studies found no time-of-day significance in any variables assessed. The magnitude of difference ranged from 2.9% to 7.1% for performance time to complete a cycling time-trial, while running and swimming did not find any differences for performance time. Power output during a 16.1-km time trial in cycling also found evening performance to be significantly better by 10%. The only other observed differences were stroke rate and stroke length during a swimming time-trial and stroke rate (cycles.min-1) during a cycling time-trial. The magnitude of difference is dependent on exercise modality, individual chronotype, the training status of the individual and sample size differences. The lack of diurnal variation present in the majority of studies can in-part be explained with some of the methodological limitations and issues present related to quality and control. It is paramount that research assessing diurnal variation in performance uses appropriate session timings around the core body temperature minimum (~05:00 h; morning) and maximum (~17:00 h; evening). Although, differences in motivation/arousal, habitual training times, chronotypes and genotypes could provide an explanation as to why some studies/variables did not display time-of-day variation, more work is needed to provide an accurate conclusion. There is a clear demand for a rigorous, standardised approach to be adopted by future investigations which control factors that specifically relate to investigations of time-of-day, such as appropriate familiarisation, counterbalancing the order of administration of tests, providing sufficient recovery time between sessions and testing within a controlled environment.
... Human motor performance varies depending on the time of day (Drust et al., 2005). The time of day in which maximum performance is reached is called acrophase, which is around 6:00 p.m. attending resistance training (Guette et al., 2005). In this regard, Grgic et al. (2019) concluded that the hypertrophy adaptations were similar regardless of the time of day the training sessions were located. ...
This umbrella review aimed to analyze the different variables of resistance training and their effect on hypertrophy, and to provide practical recommendations for the prescription of resistance training programs to maximize hypertrophy responses. A systematic research was conducted through of PubMed/MEDLINE, SPORTDiscus and Web of Science following the preferred reporting items for systematic reviews and meta-analyses statement guidelines. A total of 52 meta-analyses were found, of which 14 met the inclusion criteria. These studies were published between 2009 and 2020 and comprised 178 primary studies corresponding to 4784 participants. Following a methodological quality analysis, nine meta-analyses were categorized as high quality, presenting values of 81-88%. The remaining meta-analyses were rated as moderate quality, with values between 63-75%. Based on this umbrella review, we can state that at least 10 sets per week per muscle group is optimal, that eccentric contractions seem important, very slow repetitions (≥10s) should be avoided, and that blood flow restriction might be beneficial for some individuals. In addition, other variables as, exercise order, time of the day and type of periodization appear not to directly influence the magnitude of muscle mass gains. These findings provide valuable information for the design and configuration of the resistance training program with the aim of optimizing muscle hypertrophy.
... Diurnal variation has been shown to be ROL Spor Bilimleri Dergisi / Journal of ROL Sports Sciences 2022; 3(1): 142-153 Özgür EKEN, Ramazan BAYER 144 useful in a variety of variables affecting athletic performance, and it has been found that diurnal variation produces a variety of consequences (Bessot et al., 2006;Racinais et al., 2005). The literature confirms that there are variances in short-term athletic performance at various times of the day (Gauthier et al., 2001;Guette et al., 2005) and that this effect has an effect on athletes' performance levels (Bessot et al., 2006). According to the studies, the best short-term performance is achieved with the lowest values in the morning and the highest values in the afternoon (Sedliak et al., 2008;Souissi et al., 2010;Souissi et al., 2004). ...
Athletes frequently employ high-intensity interval training (HIIT) to improve their performance. However, it is believed that it is critical to find the most efficient time period for performing training. The purpose of this study is to assess the effect of HIIT performed at different times of the day on various performance measures. Twelve male volunteers between the ages of 18 and 25, who had been exercising three days a week for at least three years and were studying at the faculty of sports sciences, participated in the study (age, 20,67± 1,07 years; body height, 174,25± 2,34 cm; 67,58± 3,02 kg; BMI 22,34±,89). Ten minutes warm-up + ten minutes HIIT were used in the research protocols. Additionally, two measurements were taken for the HIIT program, at various times of the day (09.00-11.00 a.m in the morning; 05.00-07.00 p.m in the evening). Following each measurement, the volunteers' 30-meter sprint and T-line agility were assessed. Researchers found a statistically significant difference in the T-Test and 30 m sprint test performance between volunteers who completed the morning and evening HIIT programs (p < .05). T-Test and 30 m sprint test performances were seen greater in the evening hours. Based on the performance times of the T-Test and 30 m sprint test following the HIIT protocols performed in the morning, it was found that the HIIT protocol performed in the evening was more effective.
... Study participation required two testing sessions 48 hours apart. Testing sessions were scheduled at near identical times each day [15] and participants were asked to avoid vigorous physical activity 24 hours prior to each session. At each session, participants completed identical protocols: knee extension and flexion at three isokinetic velocities using both dynamometer systems with both limbs. ...
Purpose: The aim of this work was to determine the intersession reliability and validity of a recently developed prototype Isokinetic Knee Dynamometer to assess isokinetic knee extension and flexion peak moments compared to a Biodex System 4 dynamometer. Methods: Thirty- -five healthy participants performed two sessions (48-h separation) of bilateral concentric isokinetic knee extension and flexion on both isokinetic devices at 60 °/s (6 repetitions), 180 °/s (10 repetitions) and 240 °/s (15 repetitions). Dynamometer and limb order were randomized among participants while peak moment of each set was used for data analysis. Results: The Isokinetic Knee Dynamometer had excellent relative reliability, comparable to the System 4, and both systems displayed acceptable absolute reliability. Proportional biases were observed favoring the System 4 during knee extension of both limbs at 60 °/s and the dominant limb at 180 °/s, and fixed biases favoring the Isokinetic Knee Dynamometer in seven conditions. Relative agreement between systems was good across all test conditions with the majority demonstrating excellent agreement. Conclusions: These data support the Isokinetic Knee Dynamometer as a reliable and valid knee isokinetic testing system. Due to its reduced system complexity, space requirements, and production cost, the Isokinetic Knee Dynamometer may increase the clinical utilization of isokinetic knee assessments. Finally, these data fill an existing isokinetics literature void with the results supporting similar and acceptable measurement properties jointly for dominant and non-dominant limbs and at the higher testing velocities considered.
Physiological processes present daily oscillations of ≈24 h, called circadian rhythms. Motor performance, for example, reaches its peak in the afternoon, although this can be affected by chronotype. Certain motor activities, for example, walking, can also be affected by circadian rhythms. Healthy walking exhibits stride‐to‐stride fluctuations with a fractal‐like structure that enables adaptability. While pathology and aging are shown to lead to random‐like fluctuations; and, therefore, decreased adaptability; the influence of circadian rhythms remains unknown. This study investigates how these fluctuations present in healthy gait are affected by the time of day and chronotype. Eighteen young adults walk for 10 min every 2 h, from 8 a.m. to 6 p.m. Footswitches are used to determine heel‐strike and calculate stride time. Then, detrended fluctuation analysis is used to calculate fractal scaling. A mixed‐model Analysis of Variance is used and followed by a backward stepwise elimination process. Tukey's tests are used for pairwise comparisons. The statistical model shows the effect of time during the day (12 p.m. exhibits a higher fractal scaling compared to 8 a.m.); and chronotype (evening‐types exhibit higher fractal scaling compared to morning‐types). This study reveals the influence of chronobiology on stride‐to‐stride fluctuations. These findings open new perspectives to integrate circadian medicine in biomechanics. Gait patterns present fractal properties in their temporal structure. This feature is suggested as a measure of adaptability and is altered with aging and pathology. This study provides preliminary evidence of the effects of chronobiology on gait variability in young adults. Morning‐types present more randomness in their gait patterns, despite no significant changes across the day.
Almost all physiological and biochemical processes in the human body follow a circadian rhythm. Studies have found that the biological rhythms of the human body, especially circadian rhythms, affect the capacity for and performance of exercise. Exercise also affects circadian rhythms. The circadian rhythm influences core body temperature, muscle strength, aerobic and anaerobic exercise capacity, and flexibility. Exercise also causes a phase shift that remodels circadian rhythms. Research has shown that exercise can improve fitness if it is timed to coincide with peak performance. In addition to considering diurnal variations, preferences regarding the time of exercise (day or night) are important for studying the effects of circadian rhythms on exercise performance. Furthermore, there are differences in circadian rhythms among different exercise types. Therefore, arranging exercise time and intensity according to the characteristics of the human circadian rhythm is of great significance for improving training efficiency, reducing the occurrence of exercise injuries, and overcoming biological clock disorders.
Time-of-day influences both physical and mental performances. Its impact on motor learning is, however, not well established yet. Here, using a finger tapping-task, we investigated the time-of-day effect on skill acquisition (i.e., immediately after a physical or mental practice session) and consolidation (i.e., 24 h later). Two groups (one physical and one mental) were trained in the morning (10 a.m.) and two others (one physical and one mental) in the afternoon (3 p.m.). We found an enhancement of motor skill following both types of practice, whatever the time of the day, with a better acquisition for the physical than the mental group. Interestingly, there was a better consolidation for both groups when the training session was scheduled in the afternoon. Overall, our results indicate that the time-of-day positively influences motor skill consolidation and thus must be considered to optimize training protocols in sport and clinical domains to potentiate motor learning.
The purpose of this study was to examine the correlation between the Munich ChronoType Questionnaire (MCTQ) index and time at minimum core temperature. Nine athletes were requested to answer the MCTQ questionnaire and monitor their core temperature during night. In the MCTQ, the midpoint of sleep on free day, which is corrected for sleep debt accumulated during the workweek (MSFsc), was calculated. The core temperature was monitored using a telemetric system with an ingestible capsule-type sensor. The correlation between the MSFsc and the time at the lowest core temperature was examined. The range of MSFsc and time at minimum core temperature were 2.54–7.75 (mean ±SE: 4.54 ± 0.52, 95%CI: 3.52–5.55) and 3:43–7:41 (mean ±SE: 5:24 ± 0:32, 95%CI: 4:21–6:27), respectively. Four participants with their MSFsc later than 4.96 showed times at minimum core temperature later than 6:00. A significant correlation between the MSFsc and time at minimum core temperature was observed, with a very high correlation coefficient (r = 0.86, p < 0.01). These results suggest that the MSFsc may be useful to find athletes who have a better chance to advance their circadian rhythmicity for morning competitions.
This work provides an overview of the state of the art in the field of surface EMG for non invasive characterization of muscles and identification of CNS muscle control strategies: it is in part a tutorial and in part a review. The mechanisms of EMG signal generation, propagation, detection, processing and interpretation are briefly summarized. The main results of the European Concerted Action "Surface EMG for Non Invasive Assessment of Muscles" (SENIAM) are outlined. Specific attention is focused on the key issue of proper electrode location over the muscle, that is in between the innervation zone and the muscle tendon junction. The information content of multichannel EMG obtained with an electrode array is described and the concept of motor unit (MU) signature is explained. The recognition and classification of MU signatures during an isometric contraction strongly supports the possibility of surface EMG decomposition into the constituent (superficial) motor unit action potential trains: examples are given. Applications for monitoring myoelectric manifestations of muscle fatigue are presented as well as applications in gait analysis. Most applications of the technique are very "treacherous" and require specific competence and knowledge. The incorrect modalities of data collection and interpretation are outlined.
An English language self-assessment Morningness-Eveningness questionnaire is presented and evaluated against individual differences in the circadian vatiation of oral temperature. 48 subjects falling into Morning, Evening and Intermediate type categories regularly took their temperature. Circadian peak time were identified from the smoothed temperature curves of each subject. Results showed that Morning types and a significantly earlier peak time than Evening types and tended to have a higher daytime temperature and lower post peak temperature. The Intermediate type had temperatures between those of the other groups. Although no significant differences in sleep lengths were found between the three types, Morning types retired and arose significantly earlier than Evening types. Whilst these time significatly correlated with peak time, the questionnaire showed a higher peak time correlation. Although sleep habits are an important déterminant of peak time there are other contibutory factors, and these appear to be partly covered by the questionnaire. Although the questionnaire appears to be valid, further evaluation using a wider subject population is required.
Maximal strength tests depend on voluntary all-out efforts from subjects and so may vary with time of day. Error associated with the time of day that strength is determined may be corrected once the cosine function of the rhythm in maximum voluntary contractive (MVC) is known. The purposes of this study were to determine the magnitude of error associated with measurement of MVC at different times of day and derive an equation to correct for this. Six male subjects performed an MVC using the right knee extensors, at a knee angle of 90°. Tests were conducted at 02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 h, a minimum of 8 h separating each test. The order of testing differed between subjects. The maximal force exerted was measured with a strain-gauge assembly. Data were subjected to cosinor analysis. A significant circadian variation was found in MVC, the acrophase occurring at 17:48 h and the mean to peak variation being 7% of the mean value. These were closely in phase with the rhythm in rectal temperature (acrophase = 18:00 h; amplitude 0.4°C). By rearranging the cosine function, the MVC(corr) (corrected for time of day) can be estimated by: MVC(corr) = MVC(t)/1 + A·cos(15t+15p) where t is the time of day at which the test is performed (decimal clock hours), A is the amplitude of MVC as a % of the mean divided by 100, in this case N = 7/100 = 0.07 and p = 17.80 h. Provided the cosine characteristics of the muscle performance rhythm are known, it is proposed that this equation can be employed for other strength tests which display errors associated with time or day.
The effect of time of day on the neural activation and contractile properties of the human adductor pollicis muscle was investigated in 13 healthy subjects. Two different times of day were chosen, corresponding to the minimum (7 h) and maximum (18 h) levels of strength. The force produced was compared with the associated electromyographic (EMG) activity during voluntary and electrically induced contractions in order to determine whether peripheral or central mechanisms play a dominant role in diurnal force fluctuation. The results indicated that the force produced during a maximum voluntary contraction (MVC) was significantly higher (+8.9%) in the evening than the morning. Since the increase in force of the MVC and the tetanic contraction (100 Hz) were similar, it is suggested that peripheral mechanisms are responsible for diurnal fluctuations in force. This conclusion is supported by the observation that central activation, tested by the interpolated twitch method during an MVC, did not change, and that the EMG was less per unit force in the evening. In addition to the increase in maximum twitch and tetanus force, significant changes in muscle contractile kinetics were also observed. The maximum rate of tension development and the relaxation of the twitch and tetanus increased in the evening, and the twitch contraction time (CT) and the time to half-relaxation (TR1/2) were reduced. Because the mean range of variation in skin temperature (2.6°C) observed over the course of the day was very low, this change cannot entirely explain those observed in muscle contractile properties. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 1380–1387, 1999
Relative fibre type composition and weights of 3 forearm muscles; the m. extensor carpi radialis longus (ECRL). m. extensor carpi radialis hrevis (ECRB) and the m. bruchioradialis (BR) from both the left and right arm were determined. Fibre type 1 muscle weight of the ECRB. which cocontracts posturally during gripping, was significantly greater in the right than the left forearm. Weights of type 2 fibres in this muscle were. however, similar in the left and right arm. Fibre type weights of both ECRL and BR were also similar in both arms. For all these muscles, intra-individual co-variation in relative fibre type occurrence was found. It is proposed that genetic factors may play a role in determining the relative fibre type composition at least as far as the upper extremities are concerned. However, functional demands are also important determining factors for development of muscle structure.
Previous work has demonstrated that exercise performance varies with time of day. The aim of this study was to investigate the influence of time of day on measures of anaerobic power and anaerobic capacity. Twelve male subjects, aged 18-22 years, performed a stair run test, a standing broad jump and the Wingate Anaerobic Test on twelve separate occasions. These were at 02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 hours, duplicate measurements being obtained at each time point. Subjects' diet and activity prior to exercise and the laboratory temperature were controlled. Pre-exercise rectal temperature was measured on each occasion. The rectal temperature data conformed to a cosine function: its peak occurred at 18:11 hours and the peak to trough variation was 0.76 degrees C (p < 0.001). There was a rhythm in performance on the stair run and the broad jump tests, in phase with the curve in rectal temperature. Results for peak power and mean power production on the Wingate test did not display a significant circadian rhythm. The stair run and broad jump tests seem to be more sensitive to circadian rhythmicity than does the Wingate Anaerobic Test.
The validity and accuracy of the Biodex dynamometer was investigated under static and dynamic conditions. Static torque and angular position output correlated well with externally derived data (r = 0.998 and r greater than 0.999, respectively). Three subjects performed maximal voluntary knee extensions and flexions at angular velocities from 60 to 450 degrees.s-1. Using linear accelerometry, high speed filming and Biodex software, data were collected for lever arm angular velocity and linear accelerations, and subject generated torque. Analysis of synchronized angular position and velocity changes revealed the dynamometer controlled angular velocity of the lever arm to within 3.5% of the preset value. Small transient velocity overshoots were apparent on reaching the set velocity. High frequency torque artefacts were observed at all test velocities, but most noticeably at the faster speeds, and were associated with lever arm accelerations accompanying directional changes, application of resistive torques by the dynamometer, and limb instability. Isokinematic torques collected from ten subjects (240, 300 and 400 degrees.s-1) identified possible errors associated with reporting knee extension torques at 30 degrees of flexion. As a result of tissue and padding compliance, leg extension angular velocity exceeded lever arm angular velocity over most of the range of motion, while during flexion this compliance meant that knee and lever arm angles were not always identical, particularly at the start of motion. Nevertheless, the Biodex dynamometer was found to be both a valid and an accurate research tool; however, caution must be exercised when interpreting and ascribing torques and angular velocities to the limb producing motion.
Mechanical and electrical properties were studied for the first dorsal interosseous muscle of the dominant (d-FDI) and non-dominant hand (nd-FDI). Observations were made before, during and after a fatigue test, fatigue being evoked by percutaneous electrical stimulation of the ulnar nerve. The test consisted of 30 Hz bursts of ten supramaximal 0.1 ms pulses, repeated once a second for 5 min. The measurements included the amplitude of the first and fifth compound muscle action potentials (M-waves) within bursts, the peak burst force and the amplitude and time course of single twitches. At the end of the fatigue test, burst force had decreased to about the same extent in the FDI of both hands. The final decline in first M-wave amplitude was, however, significantly more pronounced for the nd-FDI than for the d-FDI. There were no longer any significant discrepancies between the two muscles after a subsequent recovery-period of 15 min. Comparisons among nd-FDI of various individuals demonstrated the presence of significant inter-individual differences in fatigue-related force-drop without any associated differences in M-wave decline. Intra-individual variability was similar for fatigue-related force-drop and M-wave decline.