Effect of fatigue on hamstring coactivation during isokinetic knee extensions

We examined the effect of fatigue of the quadriceps muscles on coactivation of the hamstring muscles and determined if the response is different between two isokinetic speeds in ten males and ten females with no history of knee pathology. Electromyographic data were recorded from the vastus lateralis and biceps femoris muscles during 50 maximal knee extensions at isokinetic speeds of 1.75 rad · s⁻¹ (100° · s⁻¹) and 4.36 rad · s⁻¹ (250° · s⁻¹). A greater degree of coactivation was apparent at the higher speed, but the increase in coactivation of the hamstring muscles was similar at both speeds. The results revealed that: (1) coactivation is greater at a higher isokinetic speed, and (2) coactivation increases during fatigue, but the rate of increase is independent of contraction velocity. Accepted: 15 June 1998     

Men and women show different adaptations of quadriceps activity following fatiguing contractions: An explanation for the increased incidence of sports-related knee injuries in women?

We investigated whether adaptations of quadriceps muscle activity to fatiguing exercise differs between sexes. Fifteen healthy men (age, mean ± SD; 22. ± 2.4 yr, body mass 70.5 ± 11.4 kg, height 1.72 ± 0.06 m) and 15 healthy women (age, mean ± SD; 21 ± 1.8 yr, body mass 60 ± 7.5 kg, height 1.62 ± 0.07 m), all right leg dominant, participated in the study. Participants performed a submaximal isometric knee extension contraction at 50% of the maximum voluntary contraction (MVC) sustained until task failure before and after a fatiguing exercise. Surface electromyography (EMG) was simultaneously recorded from nine regions distributed over the medial, middle and lateral locations of the quadriceps muscles in a longitudinal direction corresponding to the vastus medialis, rectus femoris (RF) and vastus lateralis muscle, respectively. A significant reduction in maximal force and time to task failure were observed after fatiguing exercise for both sexes (P < 0.001). However, women displayed greater myoelectric manifestations of fatigue specifically for the RF during the post-fatigue sustained contraction (P < 0.05). The RF is more susceptible to fatiguing exercise in women compared to men which may partly explain the higher risk of knee injuries among female athletes during competitive sports.     

Influence of the knee flexion on muscle activation and transmissibility during whole body vibration

The influence of the knee flexion on muscle activation and transmissibility during whole body vibration is controversially discussed in the literature. In this study, 34 individuals had electromyography activity (EMG) of the vastus lateralis and the acceleration assessed while squatting with 60° and 90° of knee flexion either with or without whole-body vibration (WBV). The conditions were maintained for 10 s with 1 min of rest between each condition. The main findings were (1) the larger the angle of knee flexion (90° vs. 60°), the greater the EMG (p < 0.001), with no difference on acceleration transmissibility; (2) for both angles of knee flexion, the addition of WBV produced no significant difference in EMG and higher acceleration compared to without WBV (p < 0.001). These results suggest that the larger the knee flexion angle (60° vs. 90°), the greater the muscle activation without acceleration modification. However, the addition of WBV increases the transmissibility of acceleration in the lower limbs without modification in EMG of vastus lateralis.     

On the effect of thermal agents in the response of the brachial biceps at different contraction levels

The objective of this study was to assess electromyographic features of the brachial biceps muscle after the application of cryotherapy and short-wave diathermy. Sixty healthy volunteers participated in the study and were equally divided into three groups: cryotherapy – application of ice packs for 30 min; short-wave diathermy for 20 min; and control. The thermal agents were applied to the anterior and posterior regions of the non-dominant arm. The electromyographic (EMG) signal from the brachial biceps was recorded before and after the application of thermal agents during flexion of the elbow joint at 25%, 50%, 75% of a maximum voluntary isometric contraction defined at least two days before the actual experiments (MVIC_bl). The volunteers also were asked to execute a free MVIC before and after the application of the thermal agents (MVIC_free). A linear regression model with mixed effects (random and fixed) was used. Intra-group analysis showed a reduction in root mean square (RMS) at MVIC_free, with no change in the median frequency of the EMG signal at any contraction level for the short-wave diathermy group. An increase on RMS values and a decrease on median frequencies were found after the application of cryotherapy for all contraction levels. The results imply that cryotherapy plays an important role on changing neuromuscular responses at various levels of muscle contraction. Therapists should be aware of that and carefully consider its use prior to activities in which neuromuscular precision is required.     

Patterns of hind limb motor output during walking in the salamander Dicamptodon tenebrosus,with comparisons to other tetrapods

Based on similarity of motor patterns of lizards, crocodiles, birds and mammals, various authors have concluded that a number of homologous muscles across these taxa demonstrate neuromuscular conservatism. This hypothesis remains untested for more basal taxa. Therefore, a quantitative electromyographic study of the hind limb during treadmill walking (mean speed of 0.75 SVL/s) in the salamander Dicamptodon tenebrosus was undertaken. Muscles located ventrally on the hind limb become active just before foot placement on the substrate, and maintain activity through the first half of the stance phase. Dorsally located muscles begin activity at or just before the start of the swing phase, and fire through the first half of swing. Several muscles showed a secondary EMG burst during the stride. The second burst in most ventral muscles occurred in late stance. In all dorsal muscles with double bursts, the second burst occurred in the middle of stance. Comparison of electromyographic onset and offset values for Dicamptodon to those for presumed homologues in other tetrapods reveals similarity in activity patterns for all ventral and two dorsal muscles despite anatomical rearrangements, supporting the hypothesis of neuromuscular conservatism for some muscles but not others.Abbreviations BF biceps femoris muscle - CDF caudofemoralis muscle - CPIT caudalipuboischiotibialis muscle - Dist distal - EDC extensor digitorum communis muscle - EMG electromyogram - EXF extensor cruris et tarsi fibularis muscle - EXT extensor cruris tibialis muscle - FMFB femorofibularis muscle - FPC flexor primordialis communis muscle - Gastroc gastrocnemius muscle - ILFB iliofibularis muscle - ILFM iliofemoralis muscle - ILTA extensor iliotibialis pars anterior muscle - ILTP extensor iliotibialis pars posterior muscle - ISC ischiocaudalis muscle - ISF ischioflexorius muscle - ISFM ischiofemoralis muscle - ITCR iliotrochantericus cranialis muscle - ITM iliotrochantericus medius muscle - MG medial gastrocnemius muscle - PFM pubifemoralis muscle - PIFE puboischiofemoralis externus muscle - PIFI puboischiofemoralis internus muscle - PIT puboischiotibialis muscle - Prox proximal - PTB pubotibialis muscle - Sol soleus muscle - ST semitendinosus muscle - SVL snout-vent length     

Mechanomyography of the human quadriceps muscle during incremental cycle ergometry

The mechanical activity of the human quadriceps muscle during maximal incremental cycle ergometry was investigated by mechanomyography (MMG). MMG and surface electromyography (EMG) recordings of vastus lateralis muscle activity were obtained from nine males. Cycle ergometry was performed at 60 rev/min and work load was incremented step wise by 20 W (3.2 Nm) every minute until volitional fatigue. The mean amplitudes of MMG (mMMG) and EMG (mEMG) during the contraction phase were calculated from the last six contractions in each load. The duration, load and work rate of exercise at exhaustion were 13.3 (1.6) min, 44.1 (5.5) Nm, 276.7 (34.7) W, respectively. A linear relationship between mMMG and load was evident in each subject (r = 0.868–0.995), while mEMG seemed to dissociate as the load became greater. In the grouped mean data, mMMG was linearly related to load whether aligned to the absolute (r = 0.995) or maximal (r = 0.995) load. Involvement of the noise component was further investigated by studying passive cycling by four subjects. Pedals were rotated passively for the first half of each stage (PAS) and the subject then pushed the pedals for the second half (ACT). In the lighter load region, the mMMG of ACT was as small as that of PAS. However, the change in the mMMG of PAS was very small compared with that of ACT. In conclusion, this study demonstrates a linear relationship between the mMMG of the quadriceps muscle and work load during maximal incremental cycle ergometry. The effect of movement noise was thought to be small and stable. Accepted: 22 April 1997     

Muscle activation and coactivation during five-time-sit-to-stand movement in patients undergoing total knee arthroplasty

Quadriceps weakness is prevalent with knee osteoarthritis (OA) and after total knee arthroplasty (TKA). To compensate for quadriceps dysfunction, patients often alter movement strategies. Little is known about muscle coordination during sit-to-stand (concentric) and stand-to-sit (eccentric) movements in the acute postoperative period. This investigation characterized the distribution of muscle activation between the concentric and eccentric phases during a five-time-sit-to-stand (FTSTS) movement in late stage OA and one month after TKA. Patients and healthy participants performed a FTSTS while recording bilateral ground reaction forces (GRFs) and electromyography (EMG). Concentric and eccentric ensemble averages of the GRF and EMG were calculated for the concentric and eccentric phases. Coactivation indices, integrated EMG, and GRF were calculated for each limb and phase. Patients demonstrated higher eccentric coactivation than the healthy group. Postoperative loading was higher in the nonsurgical limb. Postoperative quadriceps activity was lower in the concentric phase and higher in the eccentric phase than the healthy group. Higher coactivation in the patients resulted from sustained distribution of quadriceps activity throughout the eccentric phase. This indicated an inability to coordinate muscle firing when rapidly lowering to a chair and occurred despite unloading of the surgical limb. Although these patterns may serve as a protective strategy, they may also impede recovery of muscle function after TKA.     

Motor strategy patterns study of diabetic neuropathic individuals while walking. A wavelet approach

The aim of this study was to investigate muscle?s energy patterns and spectral properties of diabetic neuropathic individuals during gait cycle using wavelet approach. Twenty-one diabetic patients diagnosed with peripheral neuropathy, and 21 non-diabetic individuals were assessed during the whole gait cycle. Activation patterns of vastus lateralis, medial gastrocnemius and tibialis anterior were studied by means of bipolar surface EMG. The signal?s energy and frequency were compared between groups using t-test. The energy was compared in each frequency band (7–542 Hz) using ANOVAs for repeated measures for each group and each muscle. The diabetic individuals displayed lower energies in lower frequency bands for all muscles and higher energies in higher frequency bands for the extensors? muscles. They also showed lower total energy of gastrocnemius and a higher total energy of vastus, considering the whole gait cycle. The overall results suggest a change in the neuromuscular strategy of the main extensor muscles of the lower limb of diabetic patients to compensate the ankle extensor deficit to propel the body forward and accomplish the walking task.     

Diurnal Variation in Wingate-Test Performance and Associated Electromyographic Parameters

The present study was designed to evaluate time-of-day effects on electromyographic (EMG) activity changes during a short-term intense cycling exercise. In a randomized order, 22 male subjects were asked to perform a 30-s Wingate test against a constant braking load of 0.087?kg·kg^?1 body mass during two experimental sessions, which were set up either at 07:00 or 17:00?h. During the test, peak power (P_peak), mean power (P_mean), fatigue index (FI; % of decrease in power output throughout the 30 s), and evolution of power output (5-s span) throughout the exercise were analyzed. Surface EMG activity was recorded in both the vastus lateralis and vastus medialis muscles throughout the test and analyzed over a 5-s span. The root mean square (RMS) and mean power frequency (MPF) of EMG were calculated. Neuromuscular efficiency (NME) was estimated from the ratio of power to RMS. Resting core temperature, P_peak, P_mean, and FI were significantly higher (p?<?.05) in the evening than morning test (e.g., P_peak: 11.6?±?0.8 vs. 11.9?±?1 W·kg^?1). The results showed that power output decreased following two phases. During the first phase (first 20s), power output decreased rapidly and values were higher (p?<?.05) in the evening than in the morning. During the second phase (last 10s), power decreased slightly and appeared independent of the time of day of testing. This power output decrease was paralleled by evolution of the MPF and NME. During the first phase, NME and MPF were higher (p <?.05) in the evening. During the second phase, NME and MPF were independent of time of day. In addition, no significant differences were noticed between 7:00 and 17:00?h for EMG RMS during the whole 30 s. Taken together, these results suggest that peripheral mechanisms (i.e., muscle power and fatigue) are more likely the cause of the diurnal variation of the Wingate-test performance rather than central mechanisms. (Author correspondence: n_souissi@yahoo.fr)