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Abstract

This article was designed to study an interaction effect of time of day and test order-related confounding factors on daily variation in maximum muscle strength and power. Seventeen untrained men were randomized into four groups and measured at four time points (08:00 a.m., 12:00 a.m., 04:00 p.m. and 08:00 p.m.) throughout one or two days. Each groups started at different time of day in a counter-balanced order. Peak force and myoelectrical activity (EMG) of vastus medialis, vastus lateralis and biceps femoris muscles during bilateral isometric leg extension and power output during explosive dynamic leg extension was measured. Computerized muscle tonometer was used to assess resting muscle tone. Resting muscle tone did not change significantly regardless of time of day or test order. In contrast, time-of-day effect was found in force and EMG during isometric leg extension and in power output; all variables were significantly lower in the morning compared to the individual best performance/highest value achieved at any time point. In addition, the above variables were also affected by test order. Regardless of time of day, isometric force and EMG were typically highest during the first test session, while the dynamic power output gradually improved with test order. Daily variation in maximum voluntary strength and power performance could be detected despite the test order-related confounding factors.

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... The reduction in performance of quickness and accuracy of movement in the early morning seen in this study has been identified previously in strength and power tasks (17,18,19,20,21,22) as well as complex motor tasks (5). The purpose of this study was to observe the differences in performance that may occur at times that track and field athletes typically train (early in the morning or late afternoon), which in the context of a team environment is out of the control of the athletes whose training is governed by their respective coach. ...
... However, with such strong evidence for a weakened physiological state occurring in the morning, the common practice of early morning training must need to be considered. Furthermore, as well as the fact that a nadir may occur in the morning, even in the late afternoon where performance appears to be superior athletes may still not be training in their peak physiological state, which has been shown to be highly individualized and varying between 1200hr, 1500hr and 1800hr (19,20,22 Nevertheless, pre-exercise modulation of epinephrine and associated adrenergic responses will always naturally occur but a concern would be for overshooting functional needs an obviate careful control of fine motor tasks so important in many sports. This needs to be established in future research and it is our hope this research stimulates a greater interest in this line of study. ...
Article
Time of day as when to train has become an important question for many strength and conditioning specialists and this study was designed to add some insights into this complex question. The primary purpose of this investigation was to examine physical performance within the temporal context of melatonin and catecholamine concentrations in the early morning (0530hr) and late (1500hr) afternoon exercise in elite collegiate male track and field athletes (jumpers and sprinters). Subjects had a mean (±SD) age, height, and body mass of, 20.4 (±1.6) y, 185.8 (±9.4) cm, and 77.9 (±8.5) kg. Blood was obtained before each AM and PM testing session. Mean plasma melatonin concentrations were 34.9± 22.7 pg•ml and 4.8±3.3 pg•ml for the AM vs. PM trials, respectively, demonstrating a significant (P ≤ 0.05) difference between time points. Mean resting plasma epinephrine concentrations were for AM (171.7±33.7 pmol•L) than PM (127.6±47.8 pmol•L) were also significantly different between trails at the different times. In addition, significant differences were observed between AM foot quickness 5.14±1.06s s versus PM 4.39±0.76s. Mean peak power output for vertical jump power was 5407.1±1272.9 W, 5384.6±888.3 W for AM vs. PM trials respectively, which were not significantly different. The results of this investigation indicate that time of day did not negatively impact whole body physical performance responses in trained track athletes but did impact the athletic quality of quickness. Thus morning whole body power performances may be enhanced via adrenergic arousal when melatonin is elevated. However, this was not the case for movements requiring quickness and accuracy of movement. In order to compensate for the high concentrations of melatonin being secreted from the pineal gland representing a continued "sleepiness" effect on the body, early morning practices in may require greater adrenergic arousal to potentially offset melatonin's effects. The results of this study call into question using early morning practices for conditioning tasks that involve more complex movement and reaction time elements as even under aroused practice conditions.
... Maximal neuromuscular performance has been shown to fluctuate with time-of-day, with 5-15 % higher strength values observed in the evening [8,13,24,36,46] compared to the morning. However, in the case of endurance performance, the effect of diurnal rhythms seems to dissipate [11,15,17], although some studies have demonstrated that tolerance of high-intensity endurance exercise (e. g., performed as cycling) is higher in the evening [2,6]. ...
... In the present study, neuromuscular performance did not show any morning to evening fluctuation at any time point. Although this finding is in contrast to most of the previous timeof-day-specific studies [46], it is possible that the lack of diurnal variation in neuromuscular performance in the present study may have in part masked the time-of-day specific training adaptations in strength performance. ...
Article
The present study examined the effects of 24 weeks of morning vs. evening same-session combined strength (S) and endurance (E) training on neuromuscular and endurance performance. Fifty-one men were assigned to the morning (m) or evening (e) training group where S preceded E or vice versa (SEm, ESm, SEe and ESe) or to the control group. Isometric force, voluntary activation, EMG and peak wattage during the maximal cycling test were measured. Training time did not significantly affect the adaptations. Therefore, data are presented for SEm+e (SEm+SEe) and ESm+e (ESm+ESe). In the morning no order specific gains were observed in neuromuscular performance. In the evening, the changes in isometric force (SEm+e 15.9±16.7%, p=0.001; ESm+e 4.1±12.2%, p=0.615) and EMG (SEm+e 38.3±31.7%, p=0.001; ESm+e 14.67±36.44%, p=0.486) were larger ( p=0.014) in SEm+e than in ESm+e and in voluntary activation larger ( p=0.026) in SEm+e compared to controls. Peak wattage increased in the morning (SEm+e 15.9±9.2%, ESm+e 22.0±7.0%; p<0.001) and evening (SEm+e 16.3±7.2%, ESm+e 21.0±9.0%; p<0.001) but were larger (p<0.05) in ESm+e. The current training program led to greater neuromuscular adaptations when SE-training was performed in the evening, whereas the ES-training provided more optimal conditions for endurance performance adaptations both in the morning and evening. Keywords: diurnal rhythms; EMG; voluntary activation; concurrent training; muscle force
... The reduction in performance of quickness and accuracy of movement in the early morning seen in this study has been identified previously in strength and power tasks (17,18,19,20,21,22) as well as complex motor tasks (5). The purpose of this study was to observe the differences in performance that may occur at times that track and field athletes typically train (early in the morning or late afternoon), which in the context of a team environment is out of the control of the athletes whose training is governed by their respective coach. ...
... However, with such strong evidence for a weakened physiological state occurring in the morning, the common practice of early morning training must need to be considered. Furthermore, as well as the fact that a nadir may occur in the morning, even in the late afternoon where performance appears to be superior athletes may still not be training in their peak physiological state, which has been shown to be highly individualized and varying between 1200hr, 1500hr and 1800hr (19,20,22 Nevertheless, pre-exercise modulation of epinephrine and associated adrenergic responses will always naturally occur but a concern would be for overshooting functional needs an obviate careful control of fine motor tasks so important in many sports. This needs to be established in future research and it is our hope this research stimulates a greater interest in this line of study. ...
... Peripheral (Edwards et al., 2013; Guette et al., 2005a; Martin et al., 1999; Racinais et al., 2005; 13 Sedliak et al., 2008;), central (Tamm et al., 2009), or combination of both mechanisms 14 (Castaingts et al., 2004; Gauthier et al., 1996; Sedliak et al., 2011) have been proposed to explain 15 the diurnal rhythms in force production. Electromyography (EMG) and twitch interpolation 16 technique have been widely used to discriminate the involvement of peripheral and central 17 mechanisms in the diurnal variations (Chtourou & Souissi, 2012). ...
... Diurnal rhythms in maximal strength performance (Gauthier et al., 1996; Guette et al., 2005b) or higher in the evening (Callard et al., 2000; Sedliak 1 et al., 2011) when compared to the rest of the day. These controversial results can be partly 2 explained by the fact that EMG data can be affected by the muscle groups examined, as calf 3 muscles seem to have higher EMG in the morning (Guette et al., 2005b; Guette et al 2006). ...
Article
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It has been clearly established that maximal force varies during the day in human muscles but the exact mechanisms behind the diurnal rhythms are still not fully clarified. Therefore, the aim of this study was to examine the diurnal rhythms in maximal isometric force production in a large group of participants and also by separating the high morning performance types (n = 8) and the high evening performance types (n = 19) from the neutral types (n = 45) based on their actual maximal isometric force levels. Measurements were performed in the morning (7:26 h ± 63 min) and in the evening (17:57 h ± 74 min) for maximal bilateral isometric leg press force (MVCLP) together with myoelectric activity (EMGLP), maximal unilateral isometric knee extension force (MVCKE) and maximal voluntary activation level (VA%) during maximal unilateral isometric knee extension force (MVCVA) together with myoelectric activity (EMGVA). In addition, venous blood samples were drawn four times a day and serum testosterone and cortisol concentrations were analyzed. None of the participants belonged to the extreme morning or evening chronotype according to the Munich Chronotype Questionnaire. In the total group of participants, MVCLP and MVCKE were 4.4 ± 12.9% (p < 0.01) and 4.3 ± 10.6% (p < 0.01) higher in the evening compared to the morning. MVCVA and VA% did not show significant diurnal variation. The high morning performance types showed lower force values in the evening compared to the morning for MVCLP (10.8 ± 9.1%; p < 0.05) and MVCKE (5.7 ± 4.9%; p < 0.05). No significant diurnal variation was observed for MVCVA and VA%. The high evening performance types showed higher force values in the evening for MVCLP (16.1 ± 15.9%; p < 0.001), MVCKE (13.5 ± 11.3%; p < 0.001) and MVCVA (6.2 ± 9.9%; p < 0.05) with a concomitant higher VA% in the evening (p < 0.05). The neutral types showed significantly higher evening force values for the MVCLP (2.1 ± 6.7%; p < 0.05). All the other neuromuscular variables did not show significant diurnal variations. EMGLP and EMGVA did not show significant diurnal fluctuations in any group. Serum testosterone and cortisol concentrations showed normal daily rhythms with higher values observed in the morning in all of the groups (p < 0.001). Between-group differences were observed for MVCLP (p < 0.001) and MVCKE (p < 0.001) between all of the three groups. Diurnal changes in VA% differed between the high evening performance types and the neutral types (p < 0.05) and the testosterone/cortisol ratio (p < 0.05) as well as vastus lateralis EMGVA (p < 0.05) differed between the high morning and high evening performance types. In conclusion, we were able to identify the high morning performance types, the high evening performance types and the neutral types who showed significantly different diurnal rhythms in force production, irrespective of their actual chronotype. Therefore, the questionnaires designed to determine the chronotype may not always be sensitive enough to determine the "morningness" or "eveningness" in maximal neuromuscular performance. In general, central factors could partially explain the diurnal fluctuations in maximal strength performance, but peripheral mechanisms were also possibly involved.
... Resistance exercise elicits improved muscle strength and power, and elicits changes in anabolism/catabolism, depending on the time of the day. 41,42 Souissi et al 43 found that, compared to evening exercise, morning exercise yielded more beneficial effects on anaerobic performance after 6 weeks of resistance training. After examining study participants who underwent resistance training for 6 weeks in the morning, Chtourou et al 27 similarly noted that muscle performance-determined by the one-repetition, squat jump, and Wingate tests-was significantly higher among this group than among individuals who performed resistance training in the evening. ...
Data
Integrative Medicine Research j o u r n a l h o m e p a g e : w w w . i m r -j o u r n a l . o r g a b s t r a c t A growing body of evidence suggests that exercise may contribute to preventing patho-logical changes, treating multiple chronic diseases, and reducing mortality and morbidity ratios. Scientific evidence moreover shows that exercise plays a key role in improving health-related physical fitness components and hormone function. Regular exercise training is one of the few strategies that has been strictly adapted in healthy individuals and in athletes. However, time-dependent exercise has different outcomes, based on the exercise type, dura-tion, and hormone adaptation. In the present review, we therefore briefly describe the type, duration, and adaptation of exercise performed in the morning and evening. In addition, we discuss the clinical considerations and indications for exercise training.
... Resistance exercise elicits improved muscle strength and power, and elicits changes in anabolism/catabolism, depending on the time of the day. 41,42 Souissi et al 43 found that, compared to evening exercise, morning exercise yielded more beneficial effects on anaerobic performance after 6 weeks of resistance training. After examining study participants who underwent resistance training for 6 weeks in the morning, Chtourou et al 27 similarly noted that muscle performance-determined by the one-repetition, squat jump, and Wingate tests-was significantly higher among this group than among individuals who performed resistance training in the evening. ...
Article
Full-text available
A growing body of evidence suggests that exercise may contribute to preventing pathological changes, treating multiple chronic diseases, and reducing mortality and morbidity ratios. Scientific evidence moreover shows that exercise plays a key role in improving health-related physical fitness components and hormone function. Regular exercise training is one of the few strategies that has been strictly adapted in healthy individuals and in athletes. However, time-dependent exercise has different outcomes, based on the exercise type, dura-tion, and hormone adaptation. In the present review, we therefore briefly describe the type, duration, and adaptation of exercise performed in the morning and evening. In addition, we discuss the clinical considerations and indications for exercise training.
... Additionally, only peak EMG was used as a measure of muscle activity, although this has been used in previous research (Castro et al., 2013;Gribble et al., 2006;Lockie et al., 2014). EMG can also vary depending on the time of day a subject is assessed (Sedliak et al., 2011;Yang and Winter, 1983), although the researchers attempted to minimize these effects by being consistent about when the subjects were tested (i.e. the same time of day). Ankle taping may influence the timing of a muscle's peak activity (muscle latency) during a planned or reactive cut, and this should be investigated further. ...
Article
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This study investigated the effects of preventative ankle taping on planned change-of-direction and reactive agility performance and peak ankle muscle activity in basketballers. Twenty male basketballers (age = 22.30 ± 3.97 years; height = 1.84 ± 0.09 meters; body mass = 85.96 ± 11.88 kilograms) with no ankle pathologies attended two testing sessions. Within each session, subjects completed six planned and six reactive randomized trials (three to the left and three to the right for each condition) of the Y-shaped agility test, which was recorded by timing lights. In one session, subjects had both ankles un-taped. In the other, both ankles were taped using a modified subtalar sling. Peak tibialis anterior, peroneus longus (PL), peroneus brevis (PB), and soleus muscle activity was recorded for both the inside and outside legs across stance phase during the directional change, which was normalized against 10-meter sprint muscle activity (nEMG). Both the inside and outside cut legs during the change-of-direction step were investigated. Repeated measures ANOVA determined performance time and nEMG differences between un-taped and taped conditions. There were no differ-ences in planned change-of-direction or reactive agility times between the conditions. Inside cut leg PL nEMG decreased when taped for the planned left, reactive left, and reactive right cuts (p = 0.01). Outside leg PB and soleus nEMG increased during the taped planned left cut (p = 0.02). There were no other nEMG changes during the cuts with taping. Taping did not affect change-of-direction or agility performance. Inside leg PL activity was decreased, possibly due to the tape following the line of muscle action. This may reduce the kinetic demand for the PL during cuts. In conclusion, ankle taping did not signifi-cantly affect planned change-of-direction or reactive agility performance, and did not demonstrate large changes in activity of the muscle complex in healthy basketballers.
... In quiet bipedal standing, the reduction of motor output can be mainly linked to an impairment of muscle tone and/or muscle stiffness (Paillard, 2012). Time of day does not influence muscle tone (Sedliak et al., 2011), while tendon stiffness decreases in the evening as compared with the morning (Pearson & Onambele, 2006). Thus, the possible decrease of tendon stiffness of plantar extensors and flexors could at least partly explain why balance control was degraded in the last part of the day. ...
Article
Alzheimer's patients suffer from circadian dysregulation. The aim of this study was to examine the evolution of balance control and gait at different times of the day (11:00, 14:00, 18:00) in order to identify whether Alzheimer's patients were more likely to fall at certain periods of the day. Spatio-temporal parameters of centre of foot pressure displacements were measured with a force platform and spatio-temporal parameters of walking were evaluated with a gait analysis device. The results highlighted that balance control was worse in the evening and the afternoon than in the morning. Furthermore, the walking speed was faster and support duration, swing duration and cycle duration were shorter in the evening than in the morning and afternoon. The combined analysis of balance control and gait parameters revealed that balance control and walking are concomitantly altered in the evening which increases the fall risk in the evening, in comparison with the morning, for Alzheimer's patients.
... Then extend the hamstring muscles to lean forward with low resistance) (Buchheit et al, 2016). All testing was completed between 13:00 and 17:00 hours to account for the effect of circadian rhythm and to not interfere with any competitive events or matches in which the participants were involved (Sedliak et al, 2011). ...
Article
Background/Aims Foam rolling is a popular form of self-administered soft tissue therapy, commonly used in sporting environments. There are several variations in foam roller types including differences in density. No studies have examined the effects of different density type rollers on performance. This study compares the effects of varying foam roller density on hamstring flexibility and eccentric hamstring strength in active men. Methods A total of 28 healthy male participants (height 176.7 ± 5.9 cm; body mass 75.8 ± 9.6 kg; age 21.6 ± 4.0 years) were randomly allocated to receive a low density, medium density or high density foam roller or allocated to a control group. Outcome measures included hamstring flexibility through active knee extension (°) and eccentric hamstring strength pre and immediately-post foam roller application. Results Significant foam roller x time interactions were found for hamstring flexibility (P<0.05). Significant increases in active knee extension were reported post-foam roller application for all foam roller densities (P<0.05). No significant changes in strength parameters (break angle, peak and average force and torque) were found (P>0.05). No significant interactions between strength parameters, limb, type of roller or time were found (P>0.05). Conclusions Foam roller use elicits immediate positive increases in hamstring flexibility through active knee extension assessment, with the lower density foam roller displaying the largest increases in hamstring flexibility. No change in strength parameters were noted with the increases in flexibility; however, this does not denote that injury risk is reduced because of this. Findings provide practitioners with insight to inform decision making for the use of different densities of foam roller in practical settings.
... Prior to any testing all participants completed the standardised dynamic warm up protocol proposed by Comfort et al. (2019) [1], which consisted of 3 second repetitions of IMTP performance at 50%, 75% and 90% maximal efforts, each completed 60 seconds apart. All testing was completed between 13:00 and 17:00 hrs to account for the effect of circadian rhythm and in accordance with regular competition times [23]. Post-familiarisation trials all participants completed a test-retest to determine the reliability of measures on both the hand grip dynamometer and IMTP. ...
Article
Objectives. — The purpose of the present study was to analyse the association between grip strength and performance of the standardised protocol of the isometric mid-thigh pull (IMTP)test. Methods. — In total, 31 elite premier league footballers completed test—retest measures of peak force (PF) grip strength and IMTP, measures were taken 7 days apart. Post-completion of the test—retest 3 maximal IMTP and bilateral grip strength measures were taken. Mean PF was calculated bilaterally for each assessment. Linear relationships were determined for test—retest and Grip Strength Test (GST) and IMTP PF output. Results. — Test—retest of the GST and IMTP displayed significant almost perfect correlations bilaterally (P ≤ 0.001, r = 0.92—0.94, CI = 0.85—0.96). Bilateral moderate-large significant correlations were also identified between grip strength and IMTP PF (P ≤ 0.05, r = 0.54—0.72,CI = 0.30—0.86). Conclusions. — GST and IMTP are reliable and repeatable measures. Findings in the present study indicate consideration must be given to the influence of grip strength on maximal IMTPPF output. Previous literature describes standardisation procedures for IMTP performance. Pre-completion of IMTP measures in elite footballers, performance practitioners should consider assessment of the athlete’s grip strength despite the use of lifting straps.
... Subsequently, the testing session also included elements of the SAFT 90 as part of the pre-exercise warm-up, and trial repetitions of the isokinetic tasks. All testing completed between 13:00 and 17:00 hrs to account for the effects of circadian rhythm and in accordance with regular competition times (Sedliak, Haverinen, & Hakkinen, 2011). All trials were completed on the dominant lower limb, identified by their favoured kicking foot, based on non-contact musculoskeletal injury epidemiology (Brophy, Silvers, Gonzales, & Griffin, 2010). ...
Article
Eccentric hamstring strength is an aetiological risk factor for soccer injury. The temporal pattern of recovery post-exercise is critical in injury management. 18 male professional soccer players completed baseline assessments of eccentric hamstring strength at isokinetic speeds of 60, 150 and 300°· s⁻¹. Post SAFT⁹⁰ measures were repeated immediately, + 24 hrs, + 48 hrs and + 72 hrs. Main effects for recovery time and testing speed in average torque (AvT), peak torque (PT) and the corresponding angle (Ɵ) were supplemented by regression modelling to describe the temporal pattern of recovery. A main effect for isokinetic testing speed was observed in PT and AvT. A main effect for recovery time highlighted greater strength pre-exercise, with a quadratic pattern to temporal recovery highlighting minima achieved at between 40–48 hrs. Strength parameters are not fully recovered until 96 hrs post soccer specific fatigue, with implications for training design and injury management, particularly within fixture-congested periods.
... Within the present study, dynamic stability scores were observed where players were within 1 week of entering periods of PHV over the competitive season (2018-2019). Dynamic stability data was collected at the clubs training ground and all experimental measures were completed between 13:00 and 17:00 hrs to account for the effects of circadian rhythm and in accordance with regular competition times 25 . Data capture for dynamic stability negated potential learning effects 26 , as players completed previous trials of the YBT leading up to entering PHV periods. ...
Article
Background: To analyse the relationship between Peak Height Velocity (PHV) and Dynamic Balance (Y-Balance) vs non-peak growth to identify risk factors for non-contact lower limb injuries using a retrospective study design in elite youth footballers. Methods: Ninety-Three elite category 1 academy football players completed Y-Balance assessment during the preseason screening assessment. Data in relation to Y-Balance and Peak Height Velocity measures was than analysed retrospectively and correlated against injury audit data to identify relationships between the variables. Results: A significant correlation was identified between Peak Height Velocity (PHV) and measures of directional dynamic stability utilising Y-Balance assessment (p ≤ 0.001). No significant correlations were identified between PHV and injury or injury and dynamic stability scores (p > 0.05). Injury occurrence for players within predicted periods of PHV was represented as 45%, within the cohort contained within the study. Conclusions: Evidently periods of growth and maturation within elite academy footballers has a detrimental effect on directional dynamic stability performance. However, caution must be taken with interpreting the significance of this relationship and the effect it has on injury occurrence. Consideration must be given to quantifying key aetiological factors associated with injury during adolescence and refrain from reliance on measures of PHV.
... Participants completed a familiarisation trial to negate potential learning effects 21 , with all testing completed between 13:00 and 17:00 hrs to account for the effects of circadian rhythm and in accordance with regular competition times 22 . All trials were completed on the dominant lower limb, identified by their favoured kicking foot, based on non-contact musculoskeletal injury epidemiology 23 . ...
Article
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BACKGROUND Eccentric hamstring training is a contemporary approach to reducing injury risk in elite footballers. Understanding the temporal pattern of recovery would inform training design. METHODS 20 male professional football players completed baseline assessments of eccentric hamstring strength at isokinetic speeds of 60, 150 and 300°·s-1. Post-exercise assessments were repeated immediately, +24hrs, +48hrs and +72hrs. Main effects for recovery time and testing speed in average torque (AvT), peak torque (PT) and the corresponding angle (Ɵ) were supplemented by regression modelling to describe the temporal pattern of recovery. RESULTS A main effect for recovery time highlighted greater strength pre exercise, with a quadratic pattern to temporal recovery highlighting minima attained at 35.2 – 41.0 hrs. CONCLUSIONS Strength parameters are not fully recovered until 82 hrs post localised fatigue, with the angle of peak torque at high speeds recovering at a much slower rate, with implications for training design. Keywords Training, Soccer, Injury, Knee.
... Prior to any testing all participants completed a standardised warm up (5 minutes) cycling at submaximal intensity, a combination of skipping, high knees and butt kicking drills, 10 forward lunges per leg and 2 Nordic hamstring movements with low resistance (Buchheit et al. 2016). All testing was completed between 13:00 and 17:00 hrs to account for the effect of circadian rhythm and in accordance with regular competition times (Sedliak et al. 2011). ...
Article
Objectives Previous research describes dynamic stability and functional strength as key aetiological risk factors associated with lower limb non-contact musculoskeletal injury. Due to the multi factorial nature of injury risk, relationships between the two factors will inform injury management and training design. Methods Fifty-nine elite academy footballers from two English premier league category 1-status academies completed the study. All players completed measures of eccentric hamstring strength and dynamic stability. Relationships between directional stability (Anteroposterior (Ant), Posteromedial (PM) and Posterolateral (PL)) and eccentric strength metrics (PkT, AvT, PkF, AvF and Ɵ) bilaterally were identified for analysis. Results Significant correlations were identified bilaterally for functional hamstring strength metrics and PM and PL stability (P ≤. 0.05). No significant relationships were identified between anterior stability and eccentric hamstring strength parameters (P > 0.05). Conclusions Eccentric hamstring strength has a positive influence on directional stability through two planes, PM and PL. The lack of influence of eccentric hamstring strength on Ant directional stability could be attributed to increased ACL risk. Careful consideration of the significance of the relationships between eccentric hamstring strength and directional stability must be given when quantifying injury risk in elite academy footballers.
... Skeletal muscle oxidative capacity fluctuations may be driven by the circadian regulation of mitochondrial dynamics, rather than mitochondrial biogenesis (30). Diurnal patterns in functional and performance outcomes have also been reported, such as higher power and strength in the afternoon compared with in the morning, in untrained individuals (31). ...
Article
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Disruption of the skeletal muscle circadian clock leads to a preferential shift towards lipid oxidation, while reducing carbohydrate oxidation. These effects are apparent at the whole-body level, including glucose intolerance, increased energy expenditure, and fasting hyperglycemia. We hypothesize that exercise counters these metabolic disturbances by modifying the skeletal muscle clock and reverting substrate metabolism back towards an optimal substrate balance.
... All testing was completed between 13:00 and 17:00 hours to account for the effects of circadian rhythm and in accordance with regular competition times. 29 All trials were completed on the dominant lower limb, identified by their favored kicking foot, based on noncontact musculoskeletal injury epidemiology. 30 All testing was completed on the same BSS at testing level 1. ...
Article
Background: Rising injury rates within football require further understanding of the etiological risk factors associated with lower-limb injury. Aim: To examine the temporal pattern of recovery of directional dynamic stability measures post football-specific fatigue. Methods: Eighteen male elite footballers completed baseline assessments of directional dynamic stability measures (Overall Stability Index, anterior-posterior stability [A-P], medial-lateral stability [M-L] on level 1 of the Biodex Stability System). Post Soccer-Specific Aerobic Field Test90 measures were repeated immediately, +24 hours, +48 hours, and +72 hours. The main effects for the recovery time and direction of stability were supplemented by regression modeling to describe the temporal pattern of recovery. Results: Significant main effects for time were identified for all directions of stability (Overall Stability Index, A-P, and M-L) up to +48 hours postexercise (P ≤ .05). The quadratic pattern of temporal recovery highlights a minimum of 37.55 to 38.67 hours and maximum of 75.09 to 77.33 hours. Additionally, a main effect for direction of stability was observed, with significant differences identified between A-P and M-L stability at all time points (P ≤ .001). Conclusions: Reductions in directional dynamic stability +48 hours postfatigue highlight implications for training design, recovery strategies, and injury management for performance practitioners. Interestingly, A-P stability has been highlighted as being significantly reduced compared with M-L stability at all time points, regardless of the fatigue exposure. Practitioners should consider the reduction of stability in this plane in relation to common mechanisms of injury in the knee to inform injury-risk-reduction strategies.
Article
There is a lack of data on fatigue changes within 24 hours among patients with multiple sclerosis. The purpose of this study was to evaluate the effect of time of day on central and peripheral fatigue during a continuous 2-min maximal voluntary contraction of the quadriceps muscle in women and men with multiple sclerosis (MS). We studied age-matched MS patients (range, 40-50 years). The inclusion criteria for patients were: a Kurtzke Expanded Disability Status score and a Fatigue Severity Scale score. We found a significant gender difference in central activation ratio (CAR) in the evening. At the end of the 2-min maximal voluntary contraction (MVC), the voluntary torque decreased by about 65% in men and women with MS in both the morning and evening. We also observed that, in women, CAR decreased markedly during the first 30 s in the evening test. The most interesting finding of our study is that central fatigue increased, whereas peripheral fatigue decreased markedly in the evening only in women. It remains unclear why women’s central fatigue is greater in the evening than in the morning.
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The influence of time of day on elbow flexion torque was studied. Thirteen physical education students, 7 males and 6 females, made maximal and submaximal isometric contractions at 90 degrees of elbow flexors using a dynamometer. The torque developed was measured on each contraction. The myoelectric activity of the biceps muscle was also measured at the same time by surface electromyography (EMG) and quantified from the root mean square (RMS) activity. Torque and surface EMGs were measured at 6:00, 9:00, 12:00, 15:00, 18:00, 21:00, and 24:00 h over the same day. Oral temperature before each test session was measured on each occasion after a 30-min rest period. We observed a diurnal rhythm in elbow flexor torque with an acrophase at 18:00 h and a bathyphase at 6:00 h, in phase with the diurnal rhythm in oral temperature. However, the diurnal rhythm of temperature did not appear to have any influence on the torque. Links between neuromuscular efficiency and RMS/torque ratio were evaluated by measuring muscle activity along with torque. We also assessed variations in the level of maximal activity of the muscle under maximal voluntary contraction. Neuromuscular efficiency fluctuated during the day, with maximal and minimal efficiency at 18:00 h and 9:00 h, respectively, whereas activation level was maximal at 18:00 h and minimal at 9:00 h. The diurnal rhythm of torque was accounted for by variations in both central nervous system command and the contractile state of the muscle.
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We discuss current knowledge on the description, impact, and underlying causes of circadian rhythmicity in sports performance. We argue that there is a wealth of information from both applied and experimental work, which, when considered together, suggests that sports performance is affected by time of day in normal entrained conditions and that the variation has at least some input from endogenous mechanisms. Nevertheless, precise information on the relative importance of endogenous and exogenous factors is lacking. No single study can answer both the applied and basic research questions that are relevant to this topic, but an appropriate mixture of real-world research on rhythm disturbances and tightly controlled experiments involving forced desynchronization protocols is needed. Important issues, which should be considered by any chronobiologist interested in sports and exercise, include how representative the study sample and the selected performance tests are, test-retest reliability, as well as overall design of the experiment.
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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.
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The circadian rhythm in muscle strength was analysed in 12 males (28 +/- 4 years, 79.6 +/- 12.3 kg, 1.80 +/- 0.05 m) and eight females (28 +/- 4 years, 60.3 +/- 5.5 kg, 1.61 +/- 0.08 m). After two familiarization sessions, participants were tested at six different times of the day (02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 hours), the order of which was randomly assigned over 3-4 days. Rectal temperature (T(rec)) was measured over 30 min before each test. Peak isokinetic torques (PT) of knee extensors and flexors were then measured at 1.05 rad s(-1) and 3.14 rad s(-1) through a 90 degrees range of motion. Maximal isometric voluntary contraction (MVC) of knee extensors and flexors was measured at 60 degrees of knee flexion and the MVC of knee extensors was also assessed with superimposed electrical twitches (50 Hz, 250 V, 200 mus pulse width) in order to control for motivational effects. Three trials were performed in each condition, separated by 3 min recovery, and the highest values were retained for subsequent analyses. A significant circadian rhythm was observed for T(rec) in both males and females (acrophase, Phi, 17:29 and 16:40 hours; mesor, Me, 37.0 and 36.8 degrees C; amplitude, A, 0.28 and 0.33 degrees C for males and females, respectively). The mesor of T(rec) was higher in males than in females (p < 0.05). Significant circadian rhythms were observed for knee extensor PT at 3.14 rad s(-1) in males (Phi, 17:06 hours; Me, 178.2 N m; A, 4.7 N m) and for knee extensor PT at 1.05 rad s(-1) in females (Phi, 15:35 hours; Me, 128.7 N m; A, 3.7 N m). In males, the MVC of knee extensors demonstrated a significant circadian rhythm, but only when electrical twitches were superimposed (Phi, 16:17 h; Me, 302.1 N m; A, 13.6 N m). Acrophases of all indices of muscle strength were not statistically different between the two groups and were located in the afternoon (12:47 < Phi < 17:16 hours). The amplitude (percentage of mesor) of extensors MVC (electrically stimulated) was higher in males (6.4%) than in females (4.2%; p < 0.05). Significant circadian rhythms were not consistently observed for all indices of muscle strength whatever the gender. Our group of female subjects tended to show lower circadian amplitudes than the males. In males, maximal voluntary contraction of electrically stimulated muscles followed a circadian curve, which was not significant without the superimposed twitches. These results suggest that motivation could have a masking effect on the circadian rhythm in muscle performance and strengthen the view that peripheral factors are implicated in this rhythm.
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The aim of this study was to examine the time-of-day (TOD) effects in myoelectric and mechanical properties of muscle during a maximal and prolonged isokinetic exercise. Twelve male subjects were asked to perform 50 maximal voluntary contractions (MVC) of the knee extensor muscles at a constant angular velocity of 2.09 rad . sec(-1), at 06 : 00 and 18 : 00 h. Torque and electromyographic (EMG) parameters were recorded for each contraction, and the ratio between these values was calculated to evaluate variations of the neuromuscular efficiency (NME) with fatigue and with TOD. The results indicated that maximal torque values (T(45)Max) was significantly higher (7.73%) in the evening than in the morning (p<0.003). The diurnal variation in torque decrease was used to define two phases. During the first phase (1st to the 26th repetition), torque values decreased fast and values were higher in the evening than in the morning, and during the second phase (27th to the 50th repetition), torque decreased slightly and reached a floor value that appeared constant with TOD. The EMG parameters (Root Mean Square; RMS) were modified with fatigue, but were not TOD dependent. The NME decrease-significantly with fatigue, showing that peripheral factors were mainly involved in the torque decrease. Furthermore, NME decrease was greater at 18 : 00 than at 06 : 00 h for the vastus medialis (p<0.05) and the vastus lateralis muscles (p<0.002), and this occurred during the first fatigue phase of the exercise. In conclusion, the diurnal variation of the muscle fatigue observed during a maximal and prolonged isokinetic exercise seems to reflect on the muscle, with a greater contractile capacity but a higher fatigability in the evening compared to the morning.
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The possible peripheral and/or central origin in the mechanisms responsible for day-time fluctuation in maximal torque of the triceps surae muscle were investigated with a special emphasis on antagonist muscle coactivation. Eleven healthy male subjects (physical education students) took part in this investigation. The electromechanical properties of the plantar flexor muscles were recorded at two different times of day: between 06:00 h and 08:00 h in the morning and between 17:00 h and 19:00 h in the evening. To investigate peripheral mechanisms, the posterior tibial nerve was stimulated at rest, using percutaneous electrical stimuli, to evoke single twitch, double twitch, and maximal tetanic contraction (100 Hz). Maximal voluntary contraction of the plantar flexors was also assessed by means of the relative electromyographic activity of respective agonist and antagonist muscles (soleus, gastrocnemius medialis, gastrocnemius lateralis, and tibialis anterior). A double twitch was delivered during maximal voluntary plantar flexion to record muscle activation (i.e., interpolated twitch technique). The coactivation level of the tibialis anterior muscle during plantar flexion was calculated. The results indicated a significant decrease in maximal voluntary muscle torque of triceps surae in the evening as compared with the morning (-7.0 %; p < 0.05). Concerning the central command, when extrapolated by the twitch interpolation technique, the decrease in mean activation level of -6.8 % was consistent with the fluctuation in torque (-7.0 %). Soleus muscle electromyographic activity (normalized to the M-wave) showed a significant decline (21.6 %; p < 0.001). Moreover, individual changes in MVC percentage were significantly related to those of normalized electromyographic activity of the soleus muscle (r = 0.688; p < 0.01). Thus, it indicated that the subject's capacity to activate the soleus muscle was affected by the time of day. The coactivation level in the tibialis anterior muscle during plantar flexion did not change significantly in the evening. Concerning peripheral mechanisms, we observed a decrease in maximal M-wave amplitude for soleus and gastrocnemii, associated with unchanged single twitch and tetanus torque. To conclude, impairment in soleus muscle central command seemed to be the mechanism in the origin of torque failure. Such information would be of importance in the investigation of day-time fluctuations in complex motor task performances implicating the triceps surae muscle.
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The effect of the time of day on repeated cycle sprint performance and short-term recovery patterns was investigated in 12 active male subjects (23+/-2 years, 76.4+/-4.2 kg, 1.80+/-0.06 m, 9.5+/-4.5 h . week (-1) of physical activity). Subjects performed ten 6-s maximal sprints inter-spaced by 30 s rest in the morning (08 : 00-10 : 00 h) and in the evening (17 : 00-19 : 00 h) on separate days. During the intermittent exercise, peak power output (P (PO), watts), total mechanical work (W, kJ), peak pedalling rate (P (PR), rev . min (-1)), and peak efficient torque (P (TCK), Nm) were recorded. The values at the 1st, the 5th, and the 10th sprints were used as mechanical indices of fatigue occurrence. Intra-aural temperature and maximal voluntary contraction of knee extensors muscles (MVC) were measured before (pre), immediately after (post) the cycle bouts and following a 5-min passive recovery period (post 5). The MVC indices were used to further confirm occurrence of neuromuscular fatigue and to assess short-term recovery patterns from all-out intermittent effort. During the MVC, electromyographic activity of the vastus lateralis muscle was recorded and analysed as its root mean square (RMS). The torque produced per unit RMS was calculated and used as index of neuromuscular efficiency (NME). A main effect for the sprint number was observed for all cycle performance parameters (p<0.05). The main effect for the time of day was not significant for any biomechanical indices of neuromuscular performance. A significant interaction effect of the time of day and the sprint repetition was demonstrated on P (TCK) ( F(2,22)=4.3, p<0.05). The decrease in P (TCK) consecutive to sprint repetition was sharper in the evening compared to the morning (sprint 10[% of sprint 1]:-9.5 % in the evening vs. - 2.2 % in the morning, p<0.05). Significant interaction effects of the time of day and the condition (i. e. pre, post, post 5) were also demonstrated for RMS ( F(2,22)=3.6, p<0.05) and NME ( F(2,22)=4.5, p<0.05) during MVC. These interactions were characterised by similar patterns of fatigue occurrence (i. e. post vs. pre condition) in the morning (+7.5 % for RMS, - 19.6 % for NME) as in the evening (+10.2 % for RMS, -19.4 % for NME) but different patterns of short-term recovery (i. e. post 5 vs. post condition; p<0.05) in the morning (-7.3 % for RMS, +13.7 % for NME) compared to the evening (+3.3 % for RMS, -1.8 % for NME). These results suggest that short-term recovery patterns of neuromuscular function are slower in the evening compared to the morning.
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The aim of the present study was to assess the intrarater repeatability of the computerized muscle tonometer (CMT), which is a computer-driven device designed to measure and register the tone of connective tissues. The second aim was to evaluate the effect of muscle thickness on results and repeatability as well as sensitivity, which was done by comparison to a mechanical hand-held tonometer (HHT). Participants were ten healthy male volunteers. The thickness of soft tissues was measured with ultrasound and the CMT was used to evaluate the muscle tone of thigh muscles 10, 15 and 20 cm and the HHT 15 cm above the patella on both sides. Great individual variability in muscle thickness and tone was noted. Muscle thickness increased proximally on the thigh and thus the mean distance travelled by the indenter of the CMT also increased from distal to proximal from 22 to 26 mm and the work done increased from 116 to 161 mJ. Intraclass correlation (ICC) for travel and work ranged from 0.85 to 0.92 and 0.94 to 0.98, respectively. Repeatability coefficients increased somewhat at proximal measurement sites. ICC for the HHT was 0.78. The CMT also showed a considerably higher range of results, indicating greater resolution power. Despite the twofold pressure used with the HHT the distance measured was on average 60% lower compared to the CMT. In conclusion, the repeatability of the CMT was found to be good. Muscle thickness greatly affected the results and should therefore be taken into consideration when measuring muscle tone. Work was a more reliable unit of measurement than travel, which has been commonly used to describe muscle tone.
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Few data exist on the temporal relationship between catecholamines and muscle force production in vivo. The purpose of this study was to examine the influence of preexercise arousal on sympathoadrenal neurohormones on muscular force expression during resistance exercise. Ten resistance-trained men completed two experimental conditions separated by 7 days: 1) acute heavy resistance exercise protocol (AHREP; 6 x 10 repetitions parallel squats, 80% 1 repetition maximum) and 2) control (Cont; rest). Peak force (F(peak)) was recorded during a maximal isometric squat preceding each set and mean force (F(mean)) was measured during each set. Serial venous blood samples were collected before the AHREP and immediately preceding each set. Blood collection times were matched during Cont. Preexercise epinephrine (Epi), norepinephrine (NE), and dopamine (DA) increased (P <or= 0.05) above Cont by 270, 255, and 164%, respectively. During exercise, Epi, NE, and DA continued to increase by 512, 271, and 38%, respectively, above preexercise values. F(peak) and F(mean) decreased by approximately 20-25% over the course of the AHREP. Post hoc data analysis revealed that five subjects (F(maintainers)) showed no decline (P >or= 0.05) in muscular performance (F(peak), F(mean)) during AHREP and that five subjects (F(reducers)) had significant reductions in F(peak) and F(mean). Integrated area under the curve for Epi, NE, and F(peak) were greater (P < 0.02) for F(maintainers) than F(reducers). In conclusion, an anticipatory rise in catecholamines existed, which may be essential for optimal force production at the onset of exercise.
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Previous findings of time-of-day differences in athletic performance could be confounded by diurnal fluctuations in environmental and behavioral "masking" factors (e.g., sleep, ambient temperature, and energy intake). The purpose of this study was to examine whether there is a circadian rhythm in swim performance that is independent of these masking factors. Experienced swimmers (n = 25) were assessed for 50-55 consecutive hours in the laboratory. The swimmers followed a 3-h "ultra-short" sleep-wake cycle, involving 1 h of sleep in darkness and 2 h of wakefulness in dim light, that was repeated throughout the observation. The protocol distributes behavioral and environmental masking factors equally across the 24-h period. Each swimmer was scheduled to perform six maximal-effort 200-m swim trials that were distributed equally across eight times of day (n = 147 trials). Each trial was separated by 9 h. A cosine fit of intra-aural temperature data established the time of the lowest body temperature (Tmin). Swim performances were z-transformed and compared across the eight times of day and across twelve 2-h intervals relative to Tmin. Analysis of covariance, controlling for trial number, revealed a significant (P < 0.001) pattern in swim performance relative to environmental and circadian times of day. Performance peaked 5-7 h before Tmin (approximately 2300) and was worst from 1 h before to 1 h after Tmin (approximately 0500). Mean swim performance was 169.5 s; circadian variation from peak to worst performance was 5.8 s. These data suggest a circadian rhythm in athletic performance independent of environmental and behavioral masking effects.
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This study aimed to compare day-to-day repeatability of diurnal variation in strength and power. Thirty-two men were measured at four time points (07 : 00 - 08 : 00, 12 : 00 - 13 : 00, 17 : 00 - 18 : 00, and 20 : 30 - 21 : 30 h) throughout two consecutive days (day 1 and day 2). Power during loaded squat jumps, torque and EMG during maximal (MVC) and submaximal (MVC40) voluntary isometric knee extension contractions were measured. The EMG/torque ratio during MVC and MVC40 was calculated to evaluate neuromuscular efficiency. A significant time-of-day effect with repeatable diurnal patterns was found in power. In MVC, a significant time-of-day effect was present on day 2, whereas day 1 showed a typical but nonsignificant diurnal pattern. EMG and antagonist co-activation during MVC remained statistically unaltered, whereas neuromuscular efficiency improved from day 1 to day 2. A similar trend was observed in MVC40 neuromuscular efficiency with significant time-of-day and day-to-day effects. Unaltered agonist and antagonist activity during MVC suggests that modification at the muscular level was the primary source for the diurnal variation in peak torque. A learning effect seemed to affect data in MVC40. In conclusion, the second consecutive test day showed typical diurnal variation in both maximum strength and power with no day-to-day effect of cumulative fatigue.
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The aim was to evaluate the tone and electric activity of the quadriceps muscle at rest and different torque levels. The second aim was to study whether thickness of soft tissues and change in the joint position would affect muscle tone. Eighteen healthy subjects participated. Computerized muscle tonometer (CMT) and surface electromyography (sEMG) measurements were performed: seated, first at rest with leg straight and then with the knee at 60 degrees . Thereafter measurements were obtained at levels of 80, 60, 40 and 20% of the maximum isometric torque at the same knee angle. Thickness of skin, subcutis and muscle was measured by ultrasound. The CMT values taken were the depth the indenter travelled and the work it did while compressing the right rectus femoris and vastus intermedius muscles. Expressed as mean (SD) depth the change in muscle tone changed from 29.2 (3.6) mm in the relaxed position to 16.9 (5.2) mm at 80% of maximal torque, and expressed as work the values were from 1589 (150) mJ to 739 (149) mJ respectively. The correlation between CMT, sEMG and torque measurements varied from r = -0.52 to -0.71 (p < 0.01). CMT was able to detect a change of 20% in torque production and 4% in tone. Tone values, at each torque level, were significantly separate from the values at the other force levels (p < 0.001-0.04). Soft tissue thickness explained most of the tone results at rest (57%). The repeatability of the CMT measures was good (ICCs 0.75-0.99). Both depth and work correlated with electric activity and muscle torque, but the correlation with work was higher. In conclusion, muscle activity, length and thickness have to be taken into account when evaluating muscle tone.
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Time-dependent changes in elbow flexion torque have been documented according to two different sampling schedules. Seven physical education students took part in the first series of experiments, and 7 other similar subjects in the second. In both sets of experiments, the subjects performed isometric contractions: maximal and submaximal at 90° in the first experiments and maximal at different angular positions in the second. After a 30-minute rest period, the torque developed was measured at 00:00, 06:00, 09:00, 12:00, 15:00, 18:00, and 21:00h on the day of the experiment. These subjects remained in the laboratory for 24h. In the second series of experiments, the torque developed was measured at 01:00, 05:00, 09:00, 13:00, 17:00, and 21:00h over the subsequent 6 days with only one test session per day. In this case, there was an interval of 20h between two successive test sessions. In the first experiment, a significant time-of-day effect was observed for the torque of the elbow flexors under isometric conditions with an acrophase at 17:58h. The 24h normalized mean score was 92.85% with an amplitude of 7.63% of the daily mean. In the second series of experiments, there was evidence of a circadian rhythm in the torque developed by the elbow flexors at every angle position, especially at 90°, the angle investigated in the first set of experiments. The peak torque was calculated to have occurred at 17:55h. The amplitude of the rhythm was equal to 6.99% of the daily mean. There were no statistically significant differences in the characteristics of the circadian rhythm observed between the two experimental designs. We concluded that an experiment extending over several days could be employed to evaluate circadian rhythms in muscular activity reliably. (Chronobiology International, 14(3), 287–294, 1997)
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Equinovarus is the most common deformity associated with hypertonicity of the antigravity muscles in traumatic brain injury. Casting is a technique that has been used for several years in the management of spastic equinovarus. This article reviews some of the main theories on the mechanical and neurophysiological changes in muscle structure and function in the presence of spasticity. The mechanical theories reviewed are those of abnormal cross-bridge attachments; increase in sarcomere numbers; and changes in connective tissue. The neurophysiological theories examined are hyperreflexia; loss of presynaptic inhibition and normal sensory input; and reflexes induced by tactile stimulation.As each theory is discussed, hypotheses are made as to why serial casting of equinovarus deformity may have an effect on spasticity. These hypotheses are then related to evidence within literature which might support or refute each hypothesis. This review concludes that evidence indicates that in spastic equinovarus deformity both mechanical and neurophysiological factors may be involved, and that serial casting may influence the spasticity on both a mechanical and a neurophysiological basis.
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Human resting muscle (myofascial) tone (HRMT) is the passive tonus or tension of skeletal muscle that derives from its intrinsic (EMG-silent) molecular viscoelastic properties. The word tone has been used to convey varying clinical and physiological features that have led to confusion and controversy. HRMT is the vital low-level, passive tension, and resistance to stretch that contributes importantly to maintain postural stability in balanced equilibrium positions. In contrast, co-contraction of muscle is an active neuromotor control that provides greater levels of tonus for increased stabilization. Functionally, HRMT is integrated with other passive fascial and ligamentous tensional networks of the body to form a biotensegrity system. This review aims to achieve better understandings of HRMT and its functional roles.
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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.
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Day-to-day variability and single-measurement reliability of selected isokinetic knee extension-flexion strength and endurance indices were assessed in 10 adult men and 8 adult women. On three occasions separated by at least 5 days, the subjects completed 4 reciprocal maximal voluntary contractions (MVC) at different angular velocities (1.05 rad.s-1 and 3.14 rad.s-1). The men also completed a muscular endurance test consisting of 30 reciprocal, MVC at 3.14 rad.s-1. Coefficient of variation, intra-class correlation coefficient and standard error of single-measurement scores support the continued use of gravity corrected peak torque (PT) and average peak torque (APT) as indices of isokinetic leg strength. Similarly, gravity corrected APT and total work should be the recommended indices of isokinetic leg muscular endurance in men. The results suggest that these isokinetic indices must be assessed using multiple day-to-day trial protocols adequately to describe performance capacity. Composite indices such as the ratio of Knee flexion to extension PT and fatigue measurements offer considerably reduced reliability and a greater potential for misinterpretation. The reliability of knee extension indices generally exceeds that of flexion indices. Similar variability and reproducibility of responses were observed between men and women and between reciprocal contractions performed at angular velocities of 1.05 rad.s-1 and 3.14 rad.s-1.
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Two methods have been used to study the stiffness of the relaxed finger musculature after movement followed by various times at rest. The muscles stiffen considerably as the time at rest increases. The time course of this change has been plotted; it continues at a declining rate for at least 30 min. The increased stiffness after resting can be immediately reduced by active or passive movements but not by isometric efforts. These changes characterize a thixotropic system and suggest a long-term molecular rearrangement in relaxed muscle. Extensive eccentric exercise of the muscles under investigation reduces the overall stiffness and there is a concomitant increase in tremor on movement.
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: Strikingly consistent individual responses and significant mean elevations of plasma cortisol levels (5 to 9 [mu] g%) and plasma norepinephrine levels (2.0 to 2.5 [mu] g/1) were observed during a 20-min interval prior to onset of the first exhausting exercise (70% max VO2) session in eight normal young men. No detectable plasma epinephrine response was observed. Such consistent anticipatory psychoendocrine responses were not found prior to subsequent exercise sessions involving milder degrees of muscular exercise. Psychoendocrine reactions to intravenous catheterization were also observed in some individual subjects, suggesting the need for precautions to minimize the possible effects of this variable in exercise experiments. Some implications of this study for psychoendocrine research are also discussed. Copyright (C) 1973 by American Psychosomatic Society
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Three investigations were carried out to examine the concurrent validity and the reliability of a portable dynamometer (Takei Kiki Kogyo) for the measurement of back and leg strength. First, leg extension strength of 19 subjects was measured using the Takei dynamometer and compared to the isometric knee extension strength of the dominant (right) leg measured using a computer-controlled dynamometer (Lido Active, Davis, CA). The back extension strength of 18 subjects was also compared between the two dynamometers. Second, back and leg strengths of 36 subjects, aged 19-30 years, were measured twice using the Takei dynamometer. Six days separated the test and retest. Third, back and leg strengths of four subjects, aged 21-30 years, were measured at six different times of the solar day. Significant relations (p < 0.001) were obtained between the Takei and Lido dynamometers for leg strength (r = 0.90) and back strength (r = 0.79). Significant test-retest correlations (p < 0.001) were found for leg strength (r = 0.80) and back strength (r = 0.91). Group mean (+/- SD) leg strength values of test (1450.4 +/- 428.6 N) and retest (1432.8 +/- 449.1 N) did not differ ((p > 0.05). A small (4.5%) but significant difference was found between the test (1057.2 +/- 309.9 N) and retest (1106.2 +/- 334.4 N) mean values for back strength (p < 0.05). A time of day effect was evident for back and leg strength (p < 0.05); on average the peak times occurred at 16:53 h and 18:20 h, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
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With informed consent, 6 competitive tennis players performed alternate 15 "first" (emphasis-speed) serves and 15 "second" (emphasis-accuracy) serves at 09:00, 14:00 and 18:00 hours. Serve velocity was measured by the digitisation of video footage of each serve. The Hewitt Tennis Achievement Test was employed to measure the accuracy of serve. The amount of spin imparted on the ball was not measured. First serves were at all times of day faster than second serves. First serves were faster but least accurate at 18:00 hours, the time of day that body temperature and grip strength were highest. At 09:00 hours, first serves were just as accurate as second serves, even though velocity of first serves was higher. No effects for time of day were found for the speed and accuracy of second serves. These results indicate that time of day does affect the performance of tennis serves in a way that suggest a nonlinear relationship between velocity and accuracy.
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Previously, this laboratory has demonstrated that exhaustive aerobic exercise performance is not subject to significant chronobiological variation between 0800 and 2000 h, but certain physiological responses to maximal aerobic effort do fluctuate significantly within that time frame. The purpose of the present investigation was to determine whether muscle performance, and selected physiological responses to resistance exercise, was significantly influenced by time of day effects. Ten healthy, but untrained, men (21.1+/-0.6 yr, mean +/- SE) volunteered to participate in the study. In a balanced and randomized study design, each subject performed resistance exercise protocols on an isokinetic dynamometer with maximal effort at 0800 h, 1200 h, 1600 h, and 2000 h. Selected physiological and hormonal data were recorded before and immediately following the exercise stimulus. The data demonstrated significant chronobiological oscillation in peak torque, average power, maximal work in a single repetition, and total work per set. Interestingly, this oscillation was manifested only at the fastest velocities of limb movement utilized. Pre- and postexercise rectal temperature exhibited significant time of day fluctuation, as did postexercise blood pressure. Plasma levels of testosterone and cortisol also displayed significant biorhythmicity under both pre- and postexercise conditions. However, exercise-induced responses (pre- to postexercise differences) of those steroid hormones did not exhibit significant biorythmic variation. Although plasma concentrations of both testosterone and cortisol were highest at 0800 h, testosterone to cortisol ratios were greatest at 2000 h. In summary, these data suggest that maximal muscle performance does vary within the segment of the day when exercise typically occurs (0800-2000 h) but that this variation is specific to speed of movement.
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This study deals with the influence of time of day on neuromuscular efficiency in competitive cyclists during continuous exercise versus continuous rest. Knee extension torque was measured in ultradistance cyclists over a 24h period (13:00 to 13:00 the next day) in the laboratory. The subjects were requested to maintain a constant speed (set at 70% of their maximal aerobic speed obtained during a preliminary test) on their own bicycles, which were equipped with cyclosimulators. Every 4h, torque developed and myoelectric activity were estimated during maximal isometric voluntary contractions of knee extensors using an isokinetic dynamometer. Mesenteric temperature was monitored by telemetry. The same measures were also recorded while the subjects were resting awake until 13:00 the next day. During activity, torque changed within the 24h period (p < .005), with an acrophase at 19:10 and an amplitude of 7.8% around the mean of 70.7%. At rest, a circadian rhythm was observed in knee extensor torque (p < .05), with an acrophase at 19:30 and an amplitude of 6% around the mean of 92.3%. Despite the standardized conditions, the results showed that isometric maximal strength varied with time of day during both a submaximal exercise and at rest without prior exercise. The sine waves representing these two rhythms were correlated significantly. Although at rest the diurnal rhythm followed muscular activity (i.e., neurophysiological factors), during exercise, this rhythm was thought to stem more from fluctuations in the contractile state of muscle.
Article
Variations in force and electromyographic (EMG) activities of skeletal muscles with the time-of-day have been previously described, but not for a postural muscle, submitted to daily postural and locomotor tasks. In this article, mechanical performances, EMGs, and the ratio between these parameters, i.e., the neuromuscular efficiency (NME), were measured on the triceps surae (TS) of eight subjects, two times each day, at 6:00 and 18:00 h. NME was evaluated under different experimental conditions (electrically induced contractions, reflex contractions, maximal and submaximal voluntary isometric contractions, and during a natural movement, a drop jump) to determine whether mechanisms, peripheral or central in origin, were responsible for the eventual changes in NME with time-of-day. To calculate NME in induced conditions (NMEind), a supramaximal electrical stimulus was applied to the tibial nerve, and the maximal M wave of TS (TS Mmax) and the amplitude of the twitch tension (PtMmax) in response to this electrical stimulation were quantified. TS Mmax was significantly lower in the evening (mean gain value -10.7 +/- 5.5%, p < 0.05), whereas PtMmax was not significantly modified. NMEind (PtMmax/TS Mmax) was significantly higher in the evening (mean gain of 17.6 +/- 5.8%, p < 0.05), and this increase was necessarily peripheral in origin. Secondly, maximal tendon taps were applied to the Achilles tendon in order to quantify at the two times-of-day the reflexes in response to a mechanical stimulus. The maximal reflex, TS Tmax/Mmax (%), the peak amplitude of the twitch tension associated to this tendon jerk (PtTmax), and the corresponding NME (NMEreflex = PtTmax/TS Tmax/Mmax) were not affected by time-of-day, indicating that reflex excitability did not present daytime variations when tested under these conditions. Voluntary isometric contractions were required under maximal (MVC) and submaximal (25% MVC) conditions, and the corresponding torques and TS EMG were measured. MVC was higher in the evening (mean gain: 8.6 +/- 2.7%, p < 0.05) and TS EMGmax (normalized with regard to TS Mmax) also increased in the evening but not significantly; thus, NMEMvc was not modified. At 25% of MVC, TS EMG was significantly higher in the evening (mean gain of 23 +/- 13.9%, p <0.05) and a trend for a lower NME25%MVC in the evening was observed, a result probably representative of a higher muscle fatigue state in the evening. Finally, to test the muscle capacities during a natural task, a NME index was calculated during a drop jump (DJ). The NMEDJ was defined as the ratio between jump height and mean amplitude of TS EMG (% of TS Mmax) between the drop and the jump. Both jump height and NMEDJ were significantly higher in the evening (mean gains of 10.9 +/- 4.5% and 15.7 +/- 7.4%, respectively, p <0.05). In conclusion, daytime changes in the efficiency of postural muscles seem to depend on both peripheral and central mechanisms. According to the experimental conditions, NME of the postural muscle could increase, remain constant, or even decrease in the evening, and this result may reflect reverse effects of better contractile capacities and higher fatigue state.
Article
To investigate the effects of environmental temperature and the diurnal increase in body temperature on muscle contractile processes, 11 male subjects performed maximal and submaximal isometric contractions of the knee extensors with recording of the electromyographic activity in four different conditions (morning/neutral, morning/moderately warm and humid, afternoon/neutral, and afternoon/moderately warm and humid). The morning experiments were conducted between 0700 and 1900 h, and the afternoon experiments were conducted between 0500 and 0700 h. The mean laboratory temperatures and humidity were 20.5 (+/-1) degrees C + 67 (+/-4)% and 29.5 (+/-0.8) degrees C + 74 (+/-10)% for the neutral and moderately warm and humid conditions, respectively. Results showed a significant diurnal increase in both rectal and skin temperatures whatever the environmental conditions, and an increase in the skin temperature after a 60-min moderately warm exposure. The major finding of this study was an interaction effect of time of day and environmental conditions on the force/electromyographic activity ratio. That suggests that skeletal muscle contractility was differently increased by the passive warm-up effect of a moderately warm exposure, depending on the diurnal variation in body temperature. This conclusion is supported by an increase in force in the morning only after a 60-min warm exposure (+19%) and in a neutral environment only with the diurnal increase in body temperature (+12%). In summary, our data showed that both the warm exposure and the diurnal increase in body temperature influence muscle contractility and consequently muscle strength. However, the improvement in muscle contractility after these two passive warm-ups cannot be combined in order to improve force to a greater level.
Article
To examine the time-of-day (TOD) effect on torque-force/angle, fibre length (FL), tendon stiffness (K), stress, and strain using the quadriceps muscle-tendon complex as a model. Twelve healthy young men (aged 27+/-2.0 years) were studied at AM (7h45) and PM (5h45). Maximal isometric contractions were carried out on an isokinetic dynamometer, with real-time recordings of vastus lateralis (VL) FL and patella tendon K using B-mode ultrasonography. Percutaneous electrical twitch doublets superimposed on maximal torque were used to test for muscle activation capacity (AC). At PM, torque and force increased by 16+/-3.0% (P<0.01) over 30-90 degrees knee angles. Where the load was standardised (at 250N) in order to discriminate between torque generation capacity and tendon K changes, PM relative to AM, there were 8% and 13% (P<0.01) reductions in relaxed and contracted FL, respectively. Average K decreased by 21% (P<0.001) and the maximal stress and strain were increased at PM by 11% and 16%, respectively (P<0.01). No TOD effect on AC was seen. The quadriceps torque or force-angle relationships shift upwards at PM vs. AM, with no shift in the position of the optimal knee angle. This torque or force increase appears not to be centrally modulated. Although K decreases with TOD thereby potentially shortening the working length of the sarcomeres, these changes overall do not affect the ability of the muscle to produce greater torque in the evening.
Article
A time-of-day influence on the neuromuscular response to strength training has been previously reported. However, no scientific study has examined the influence of the time of day when strength training is performed on hormonal adaptations. Therefore, the primary purpose of this study was to examine the effects of time-of-day-specific strength training on resting serum concentrations and diurnal patterns of testosterone (T) and cortisol (CORT) as well as maximum isometric strength of knee extensors. Thirty eight diurnally active healthy, previously untrained men (age 20-45 yrs) underwent a ten-week preparatory strength training period when sessions were conducted between 17:00-19:00 h. Thereafter, these subjects were randomized into either a morning (n=20, training times 07:00-09:00 h) or afternoon (n=18, 7:00-19:00 h) training group for another ten-week period of time-of-day-specific training (TST). Isometric unilateral knee extension peak torque (MVC) was measured at 07:00, 12:00, 17:00, and 20:30 h over two consecutive days (Day 1 & Day 2) before and after TST. Blood samples were obtained before each clock-time measurement to assess resting serum T and CORT concentrations. A matched control group (n=11) did not train but participated in the tests. Serum T and CORT concentrations significantly declined from 07:00 to 20:30 h on all test days (Time effect, p<.001). Serum CORT at 07:00 h was significantly higher on Day 1 than Day 2 in the control and afternoon group, both in Pre and Post conditions (Day x Time interaction, p<.01). In the morning group, a similar day-to-day difference was present in the Pre but not Post conditions (Time x Group interaction, p<.05). MVC significantly increased after TST in both the morning and afternoon groups (Pre to Post effect, p<.001). In both groups, a typical diurnal variation in MVC (Time effect, p<.001) was found, especially on Day 2 in the Pre condition, and this feature persisted from Pre to Post in the afternoon group. In the morning group, however, diurnal variation was reduced after TST on both Day 1 and Day 2 (Pre to PostxDay x TimexGroup interaction, p<.05). In conclusion, 10 weeks of morning time-of-day-specific strength training resulted in reduced morning resting CORT concentrations, presumably as a result of decreased masking effects of anticipatory psychological stress prior to the morning testing. The typical diurnal pattern of maximum isometric strength was blunted by the TST period in the morning but not the afternoon group. However, the TST period had no significant effect on the resting total T concentration and its diurnal pattern and on the absolute increase in maximum strength.