Gender differences in skeletal muscle fatigability are related to contraction type and EMG spectral compression.

The purposes of this study were 1) to evaluate gender differences in back extensor endurance capacity during isometric and isotonic muscular contractions, 2) to determine the relation between absolute load and endurance time, and 3) to compare men [n = 10, age 22.4 +/- 0.69 (SE) yr] and women (n = 10, age 21.7 +/- 1.07 yr) in terms of neuromuscular activation patterns and median frequency (MF) shifts in the electromyogram (EMG) power spectrum of the lumbar and hip extensor muscles during fatiguing submaximal isometric trunk extension exercise. Subjects performed isotonic and isometric trunk extension exercise to muscular failure at 50% of maximum voluntary contraction force. Women exhibited a longer endurance time than men during the isometric task (146.0 +/- 10.9 vs. 105.4 +/- 7.9 s), but there was no difference in endurance performance during the isotonic exercise (24.3 +/- 3.4 vs. 24.0 +/- 2.8 repetitions). Absolute load was significantly related to isometric endurance time in the pooled sample (R(2) = 0.34) but not when men and women were analyzed separately (R(2) = 0.05 and 0.04, respectively). EMG data showed no differences in neuromuscular activation patterns; however, gender differences in MF shifts were observed. Women demonstrated a similar fatigability in the biceps femoris and lumbar extensors, whereas in men, the fatigability was more pronounced in the lumbar musculature than in the biceps femoris. Additionally, the MF of the lumbar extensors demonstrated a greater association with endurance time in men than in women (R(2) = 0.45 vs. 0.19). These findings suggest that gender differences in muscle fatigue are influenced by muscle contraction type and frequency shifts in the EMG signal but not by alterations in the synergistic activation patterns.     

Gender alters impact of hypobaric hypoxia on adductor pollicis muscle performance.

Recently, we reported that, at similar voluntary force development during static submaximal intermittent contractions of the adductor pollicis muscle, fatigue developed more slowly in women than in men under conditions of normobaric normoxia (NN) (Acta Physiol Scand 167: 233-239, 1999). We postulated that the slower fatigue of women was due, in part, to a greater capacity for muscle oxidative phosphorylation. The present study examined whether a gender difference in adductor pollicis muscle performance also exists during acute exposure to hypobaric hypoxia (HH; 4,300-m altitude). Healthy young men (n = 12) and women (n = 21) performed repeated static contractions at 50% of maximal voluntary contraction (MVC) force of rested muscle for 5 s followed by 5 s of rest until exhaustion. MVC force was measured before and at the end of each minute of exercise and at exhaustion. Exhaustion was defined as an MVC force decline to 50% of that of rested muscle. For each gender, MVC force of rested muscle in HH was not significantly different from that in NN. MVC force tended to decline at a faster rate in HH than in NN for men but not for women. In both environments, MVC force declined faster (P < 0.01) for men than for women. For men, endurance time to exhaustion was shorter (P < 0.01) in HH than in NN [6.08 +/- 0.7 vs. 8.00 +/- 0.7 (SE) min]. However, for women, endurance time to exhaustion was similar (not significant) in HH (12.86 +/- 1.2 min) and NN (13.95 +/- 1.0 min). In both environments, endurance time to exhaustion was longer for women than for men (P < 0.01). Gender differences in the impact of HH on adductor pollicis muscle endurance persisted in a smaller number of men and women matched (n = 4 pairs) for MVC force of rested muscle and thus on submaximal absolute force and, by inference, ATP demand in both environments. In contrast to gender differences in the impact of HH on small-muscle (adductor pollicis) exercise performance, peak O(2) uptake during large-muscle exercise was lower in HH than in NN by a similar (P > 0.05) percentage for men and women (-27.6 +/- 2 and -25.1 +/- 2%, respectively). Our findings are consistent with the postulate of a higher adductor pollicis muscle oxidative capacity in women than in men and imply that isolated performance of muscle with a higher oxidative capacity may be less impaired when the muscle is exposed to HH.     

Muscle metabolism during prolonged exercise in humans: influence of carbohydrate availability.

Eight endurance-trained men cycled to volitional exhaustion at 69 +/- 1% peak oxygen uptake on two occasions to examine the effect of carbohydrate supplementation during exercise on muscle energy metabolism. Subjects ingested an 8% carbohydrate solution (CHO trial) or a sweet placebo (Con trial) in a double-blind, randomized order, with vastus lateralis muscle biopsies (n = 7) obtained before and immediately after exercise. No differences in oxygen uptake, heart rate, or respiratory exchange ratio during exercise were observed between the trials. Exercise time to exhaustion was increased by approximately 30% when carbohydrate was ingested [199 +/- 21 vs. 152 +/- 9 (SE) min, P < 0.05]. Plasma glucose and insulin levels during exercise were higher and plasma free fatty acids lower in the CHO trial. No differences between trials were observed in the decreases in muscle glycogen and phosphocreatine or the increases in muscle lactate due to exercise. Muscle ATP levels were not altered by exercise in either trial. There was a small but significant increase in muscle inosine monophosphate levels at the point of exhaustion in both trials, and despite the subjects in CHO trial cycling 47 min longer, their muscle inosine monophosphate level was significantly lower than in the Con trial (CHO: 0.16 +/- 0.08, Con: 0.23 +/- 0.09 mmol/kg dry muscle). These data suggest that carbohydrate ingestion may increase endurance capacity, at least in part, by improving muscle energy balance.     

Gender differences in methamphetamine use and responses: A review

Background: Men and women differ markedly with regard to their use of, and responses to, methamphetamine (MA) and related amphetamines. However, these gender differences oftentimes are given only a cursory consideration in the analyses of these MA effects.Objective: In this brief review, we summarize the data on gender differences in various parameters of MA use and responses. Such information on the pattern of male versus female differences in the use and responses to this psychostimulant can aid in tailoring gender-dependent treatment strategies.Methods: English-language articles were identified from MEDLINE as well as from reference lists of identified articles for the years 1966 to 2007. Search terms included various combinations of men/male, women/female, methamphetamine, and gender/sex differences. Only studies with human subjects were reviewed.Results: Women tend to begin MA use at earlier ages, appear more dependent on MA, but also respond better to treatment than do men. MA use appears to be associated with depression in women, and women seem more committed to MA, whereas men are more likely to use other drugs in the absence of access to MA. Female MA abusers had both larger volumes within the corpus callosum and more hyperperfused regions in the parietal and occipital areas of the brain, along with more genetic alterations but less MA-induced toxicity. Amphetamine-stimulated dopamine release was greater in men.Conclusions: When considered in total, women seem more dependent on and committed to MA but show diminished (amphetamine-stimulated) dopamine responses and a decreased degree of toxicity, as indicated by a lower incidence of emergency department-related deaths involving MA. A pervasive comorbidity of depression or depression-related characteristics were present in women MA users, suggesting that MA may serve as a type of self-medication for their depression. These findings not only highlight the need for consideration of gender when assessing MA use, but also can serve to direct efforts at prevention and treatment programs that address the specific needs of men and women.     

Dietary carbohydrate, muscle glycogen content, and endurance performance in well-trained women.

This study examined the ability of well-trained eumenorrheic women to increase muscle glycogen content and endurance performance in response to a high-carbohydrate diet (HCD; approximately 78% carbohydrate) compared with a moderate-carbohydrate diet (MD; approximately 48% carbohydrate) when tested during the luteal phase of the menstrual cycle. Six women cycled to exhaustion at approximately 80% maximal oxygen uptake (VO(2 max)) after each of the randomly assigned diet and exercise-tapering regimens. A biopsy was taken from the vastus lateralis before and after exercise in each trial. Preexercise muscle glycogen content was high after the MD (625.2 +/- 50.1 mmol/kg dry muscle) and 13% greater after the HCD (709.0 +/- 44.8 mmol/kg dry muscle). Postexercise muscle glycogen was low after both trials (MD, 91.4 +/- 34.5; HCD, 80.3 +/- 19.5 mmol/kg dry muscle), and net glycogen utilization during exercise was greater after the HCD. The subjects also cycled longer at approximately 80% VO(2 max) after the HCD vs. MD (115:31 +/- 10:47 vs. 106:35 +/- 8:36 min:s, respectively). In conclusion, aerobically trained women increased muscle glycogen content in response to a high-dietary carbohydrate intake during the luteal phase of the menstrual cycle, but the magnitude was smaller than previously observed in men. The increase in muscle glycogen, and possibly liver glycogen, after the HCD was associated with increased cycling performance to volitional exhaustion at approximately 80% VO(2 max).     

Increases in maximal accumulated oxygen deficit after high-intensity interval training are not gender dependent.

Gender differences in maximal accumulated oxygen deficit (MAOD) were examined before and after 4 and 8 wk of high-intensity interval training. Untrained men (n = 7) and women (n = 7) cycled at 120% of pretraining peak oxygen uptake (VO2 peak) to exhaustion (MAOD test) pre-, mid-, and posttraining. A posttraining timed test was also completed at the MAOD test power output, but this test was stopped at the time to exhaustion achieved during the pretraining MAOD test. The 14.3 +/- 5.2% increase in MAOD observed in men after 4 wk of training was not different from the 14.0 +/- 3.0% increase seen in women (P > 0.05). MAOD increased by a further 6.6 +/- 1.9% in men, and this change was not different from the additional 5.1 +/- 2.3% increase observed in women after the final 4 wk of training. VO2 peak measured during incremental cycling increased significantly (P < 0.01) in male but not in female subjects after 8 wk of training. Moreover, the accumulated oxygen (AO2) uptake was higher in men during the posttraining timed test compared with the pretraining MAOD test (P < 0.01). In contrast, the AO2 uptake was unchanged from pre- to posttraining in female subjects. The increase in MAOD with training was not different between men and women, suggesting an enhanced ability to produce ATP anaerobically in both groups. However, the increase in VO2 peak and AO2 uptake obtained in male subjects after training indicates improved oxidative metabolism in men but not in women. We conclude that there are basic gender differences that may predispose men and women to specific metabolic adaptations after a period of intense interval training.     

Early inequalities in excellent health and performance among young adult women and men in Sweden

Background: Although health inequality between young adult women and men has been strikingly evident in symptoms of ill health, we found no studies examining these inequalities with a focus on positive health and performance.Objective: The aim of the present study was to examine possible inequalities between young adult women and men in a combined assessment of positive health and health-related performance.Methods: Women and men aged 18 to 25 years studying medicine or computer science at 6 colleges/universities in 5 cities in Sweden were recruited for this study. All respondents answered a Web-based questionnaire regarding health, health-related performance, information and communication technology exposure, mood, and individual factors. A combined assessment of excellent health and health-related performance (EHHP) was defined and tested. Prevalence ratios (PRs) with 95% CIs of EHHP were calculated separately for female and male respondents. To assess potential determinants of EHHP, differences in the relationships between EHHP and the explanatory factors were compared for both sexes.Results: In a study group of young adult students consisting of 1046 women and 1312 men, women were less likely than men to have EHHP (PR 0.90 [95% CI, 0.83–0.98]). This inequality was even stronger within each course of study (medicine or computer science). Health-related factors showed similar patterns of relationship to EHHP for women and men; however, the strength of these relationships differed between the sexes. Logical relationships were observed between EHHP and almost all of the symptoms as well as between EHHP, the mood index, and health-related behavior.Conclusions: The well-known inequality in symptoms of ill health between young adult women and men was prevalent even in a combined assessment of positive health and health-related performance. That this inequality was prevalent in a relatively homogeneous sample of young adults indicates the importance of gender-based psychological and psychosocial factors beyond the more well-known structural gender-differentiating factors of vertical and horizontal segregation and disproportional responsibilities for domestic work. It may therefore be essential to emphasize these gender-based psychological and psychosocial factors when designing future studies and health promotion programs.     

Muscle oxygenation during incremental arm and leg exercise in men and women

The purpose of this study was to compare the rates of muscle deoxygenation in the exercising muscles during incremental arm cranking and leg cycling exercise in healthy men and women. Fifteen men and 10 women completed arm cranking and leg cycling tests to exhaustion in separate sessions in a counterbalanced order. Cardiorespiratory measurements were monitored using an automated metabolic cart interfaced with an electrocardiogram. Tissue absorbency was recorded continuously at 760 nm and 850 nm during incremental exercise and 6 min of recovery, with a near infrared spectrometer interfaced with a computer. Muscle oxygenation was calculated from the tissue absorbency measurements at 30%, 45%, 60%, 75% and 90% of peak oxygen uptake (V˙O₂) during each exercise mode and is expressed as a percentage of the maximal range observed during exercise and recovery (%Mox). Exponential regression analysis indicated significant inverse relationships (P < 0.01) between %Mox and absolute V˙O₂ during arm cranking and leg cycling in men (multiple R = −0.96 and −0.99, respectively) and women (R =−0.94 and −0.99, respectively). No significant interaction was observed for the %Mox between the two exercise modes and between the two genders. The rate of muscle deoxygenation per litre of V˙O₂ was 31.1% and 26.4% during arm cranking and leg cycling, respectively, in men, and 26.3% and 37.4% respectively, in women. It was concluded that the rate of decline in %Mox for a given increase in V˙O₂ between 30% and 90% of the peak V˙O₂ was independent of exercise mode and gender. Accepted: 31 March 1998     

Gender Differences in patient-provider symptom agreement in reporting respiratory complaints on a questionnaire

Background: Men and women communicate differently, but it is unclear whether this influences health care outcomes.Objective: Because women patients frequently choose women health care providers, we examined whether this preference was affected by communication styles. We focused on communication of disease-specific symptoms, hypothesizing that symptom agreement between women patients and women health care providers would be greater than between other patient-provider gender combinations.Methods: Patients attending outpatient clinics were recruited as part of a study of respiratory illness at 7 university-affiliated sites during 3 consecutive influenza seasons (2000–2003). Individuals aged ≥ 19 years were offered enrollment if they sought care for cold or flu symptoms at a participating study site. Patients were eligible to participate in the study if they reported any 1 of 6 symptoms: cough, runny nose, fever (subjective), muscle aches, sore throat, and/or exhaustion. Using separate questionnaires, patients and their health care providers recorded the patients' respiratory symptoms (as present or absent). Patients recorded their symptoms before visiting their health care provider, and providers recorded patient symptoms after the visit. Symptom agreement was compared using general estimating equations across all gender combinations.Results: A total of 327 patients (220 women, 107 men) and 84 health care providers (37 women, 47 men) participated in the study. Overall symptom agreement for all patient-provider gender combinations was 81.9% (95% CI, 79.6%–84.2%). For each symptom, the observed agreement significantly exceeded the agreement expected by chance alone (P < 0.001 for all symptoms except “no energy,” which was P = 0.023). The male-male pairing of patient and provider was more likely to agree on a symptom than were the other gender combinations, although not statistically significantly more so than the female-female pairing.Conclusions: In this survey of patients with respiratory illness, there was no significant difference in symptom agreement for most symptoms between the male-male and female-female patient-provider combinations. Based on these findings, symptom agreement alone does not explain why women patients select women health care providers.     

Effect of carbohydrate ingestion on glucose kinetics and muscle metabolism during intense endurance exercise.

There has been recent interest in the potential performance and metabolic effects of carbohydrate ingestion during exercise lasting approximately 1 h. In this study, 13 well-trained men ingested in randomized order either a 6% glucose solution (CHO trial) or a placebo (Con trial) during exercise to exhaustion at 83+/-1% peak oxygen uptake. In six subjects, vastus lateralis muscle was sampled at rest, at 32 min, and at exhaustion, and in six subjects, glucose kinetics was determined by infusion of [6,6-(2)H]glucose in both trials and ingestion of [6-(3)H]glucose in the CHO trial. Of the 84 g of glucose ingested during exercise in the CHO trial, only 22 g appeared in the peripheral circulation. This resulted in a small (12 g) but significant (P<0.05) increase in glucose uptake without influencing carbohydrate oxidation, muscle glycogen use, or time to exhaustion (CHO: 68.1+/-4.1 min; Con: 69.6+/-5.5 min). Decreases in muscle phosphocreatine content and increases in muscle inosine monophosphate and lactate content during exercise were similar in the two trials. Although endogenous glucose production during exercise was partially suppressed in the CHO trial, it remained significantly above preexercise levels throughout exercise. In conclusion, only 26% of the ingested glucose appeared in the peripheral circulation. Glucose ingestion increased glucose uptake and partially reduced endogenous glucose production but had no effect on carbohydrate oxidation, muscle metabolism, or time to exhaustion during exercise at 83% peak oxygen uptake.     

Effects of Local and Remote Muscle Pain on Stretch ReflexActivities in the Elbow Joint Flexors and Extensors of Unanesthetized Cats

In experiments on unanesthetized cats, we compared the effects of experimentally induced pain in the m. biceps brachii or in the neck muscles on EMG activity of the flexors and extensors of the elbow joint (mm. biceps et triceps brachii, respectively) evoked by a passive extension-flexion of the above joint. Muscle pain was induced by injections of 0.5 ml of a hypertonic (7%) NaCl solution into the above-mentioned muscles. In the case of pain in the biceps, i.e., in the muscle directly involved in realization of the reflex, we observed an increase in the amplitude and significant shortening of the latency of EMG responses of this muscle. The amplitude of a short-latency (supposedly monosynaptic) component of the biceps reflex (М1 response) increased by 65%, while an increment of the latter (supposedly polysynaptic) М2 component was 117%. When pain was induced in anatomically remote neck muscles, the stretch reflex in the biceps was considerably suppressed. The maximum amplitudes of the М1 and М2 components decreased by 25 and 30%, respectively, but the latencies of these components decreased significantly, similarly to what was observed in the case of induction of experimental pain in the biceps. Under both conditions of experimental pain, changes in the parameters of EMG responses of the forearm extensor (m. triceps brachii) demonstrated similarity with those of the biceps responses. The maximum effect of pain induction was observed within the first 5 min after injections of the hypertonic solution; full recovery of the stretch reflex parameters was observed on the 20th to 30th min. We conclude that the effects of pain induction on the reflex under study are not generalized. They depend on the site of such induction with respect to the muscle where the stretch reflex is elicited. Unidirectional effects of both types of pain on the antagonist muscles allow us to suppose that modulation of the reflex reactions upon pain induction is mediated by influences from the supraspinal CNS structures. Induction of pain in the biceps increased the amplitude of EMG manifestations of the stretch reflex, while such induction in the neck muscles decreased such responses; nonetheless, in both cases the latency of the reflexes decreased. This fact allows us to believe that the sensitivity of muscle spindles increased under both conditions of the pain influence.     

女子拳击运动员上肢和腰部肌肉力量训练的肌电分析

目的：利用肌电指标分析拳击运动员上肢和腰部肌肉力量训练效果。方法：用Mega公司的ME6000肌电图仪记录分析10名女子拳击运动员上臂肱二头肌（主动肌）与肱三头肌（拮抗肌）、前臂屈肌（主动肌）与伸肌（拮抗肌）和腰部肌群的运动诱发肌电,规定运动为手持2.5 kg的哑铃负荷进行直拳空击运动直至局部肌肉力竭。结果：直拳空击运动至局部肌肉力竭过程中,上肢拮抗肌的中位频率（MF）下降幅度和速度大于相对应的主动肌,且从肌群作功来看,主动肌作功百分比较拮抗肌大。其中9名普通运动员腰肌的肌电频率（MF）均值较1名指定样本世界冠军的下降缓慢,而且其作功百分比都较小。结论：通过对普通女子拳击运动员上肢和腰部肌群肌电指标测试与世界冠军的比较分析,提示本研究中所测普通拳击运动员拮抗肌和腰部肌肉力量训练不足,有待加强该部肌肉的力量训练。     

Long-term activity in upper- and lower-limb muscles of humans.

Despite limited data on humans, previous studies suggest that there is an association between the duration of daily muscle activity and the proportion of type I muscle fibers. We quantified the activity of limb muscles in healthy men and women during normal use and compared these measurements with published reports on fiber-type proportions. Seven men (age range = 21-28 yr) and seven women (age range = 18-26 yr) participated in two 10-h recording sessions. Electromyogram (EMG) activity of four muscles in nondominant upper (first dorsal interosseus and biceps brachii) and lower limbs (vastus medialis and vastus lateralis) was recorded with surface electrodes. Hand and arm muscles were active for 18% of the recording time, whereas leg muscles were active for only 10% of the recording time. On average, upper-limb muscles were activated 67% more often than lower-limb muscles. When lower-limb muscles were activated, however, the mean amplitude of each burst was greater in leg muscles [18 and 17% maximum voluntary contraction (MVC)] compared with hand (8% MVC) and arm (6% MVC) muscles. Temporal association in activity between pairs of muscles was high for the two lower-limb muscles (r2 = 0.7) and relatively weak for the two upper-limb muscles (r2 = 0.09). Long-term muscle activity was only different between men and women for the biceps brachii muscle. We found no relation between duration of muscle activity in 10-h recordings and the reported values of type I fibers in men and women.     

Pilot study of inflammatory responses following a negative imaginal focus in persons with chronic pain: Analysis by sex/gender

Background: Recent evidence suggests that differential stress and immune responses may play a role in the sex/gender disparity for pain. Pain pathology and psychological stress are both associated with elevated levels of proinflammatory cytokines.Objective: This pilot study tested a negative imaginal focus to assess whether it would elicit a proinflammatory cytokine response and whether responses would vary by sex/gender.Methods: Adults with chronic musculoskeletal pain were recruited from an outpatient, multidisciplinary pain clinic in Portland, Oregon, between 2007 and 2008. All participants underwent a psychologist-guided 10-minute focus on the negative aspects of their pain condition and the imagined worsening of their pain; no control group was used. Serum collected at baseline and postfocus (1, 2, and 2.5 hours) was assayed for interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). Cortisol was assayed at each time point and at 15 minutes postfocus.Results: Thirty-six outpatients (aged 26-62 years; 23 women, 13 men) participated in the study. Compared with men, women displayed greater negative emotional expression during the experiment, and this in turn mediated their IL-6 inflammatory responses. Relative to men, the IL-6 response trajectory was delayed for women. The IL-6 and TNF-a findings suggest women's maximal cytokine responses were not captured by the final time point.Conclusions: This pilot study provides preliminary evidence that women with chronic pain may experience increased and delayed inflammatory responses following negative emotional expression induced by thinking negatively about their pain condition. The findings have implications for pain catastrophizing research. This early-phase research suggests that the timing and duration of the cytokine response are critical factors to consider in future pain research.     

Gender differences in insulin resistance,body composition,and energy balance

Background: Men and women differ substantially in regard to degrees of insulin resistance, body composition, and energy balance. Adipose tissue distribution, in particular the presence of elevated visceral and hepatic adiposity, plays a central role in the development of insulin resistance and obesity-related complications.Objective: This review summarizes published data on gender differences in insulin resistance, body composition, and energy balance, to provide insight into novel gender-specific avenues of research as well as gender-tailored treatments of insulin resistance, visceral adiposity, and obesity.Methods: English-language articles were identified from searches of the PubMed database through November 2008, and by reviewing the references cited in these reports. Searches included combinations of the following terms: gender, sex, insulin resistance, body composition, energy balance, and hepatic adipose tissue.Results: For a given body mass index, men were reported to have more lean mass, women to have higher adiposity. Men were also found to have more visceral and hepatic adipose tissue, whereas women had more peripheral or subcutaneous adipose tissue. These differences, as well as differences in sex hormones and adipokines, may contribute to a more insulin-sensitive environment in women than in men. When normalized to kilograms of lean body mass, men and women had similar resting energy expenditure, but physical energy expenditure was more closely related to percent body fat in men than in women.Conclusion: Greater amounts of visceral and hepatic adipose tissue, in conjunction with the lack of a possible protective effect of estrogen, may be related to higher insulin resistance in men compared with women.     

Limb and sex-related differences in knee muscle co-contraction exist 3 months after anterior cruciate ligament reconstruction

Interlimb and sex-based differences in gait mechanics and neuromuscular control are common after anterior cruciate ligament reconstruction (ACLR). Following ACLR, individuals typically exhibit elevated co-contraction of knee muscles, which may accelerate knee osteoarthritis (OA) onset. While directed (medial/lateral) co-contractions influence tibiofemoral loading in healthy people, it is unknown if directed co-contractions are present early after ACLR and if they differ across limbs and sexes. The purpose of this study was to compare directed co-contraction indices (CCIs) of knee muscles in both limbs between men and women after ACLR. Forty-five participants (27 men) completed overground walking at a self-selected speed 3 months after ACLR during which quadriceps, hamstrings, and gastrocnemii muscle activities were collected bilaterally using surface electromyography. CCIs of six muscle pairs were calculated during the weight acceptance interval. The CCIs of the vastus lateralis/biceps femoris muscle pair (lateral musculature) was greater in the involved limb (vs uninvolved; p = 0.02). Compared to men, women exhibited greater CCIs in the vastus medialis/lateral gastrocnemius and vastus lateralis/lateral gastrocnemius muscle pairs (p < 0.01 and p = 0.01, respectively). Limb- and sex-based differences in knee muscle co-contractions are detectable 3 months after ACLR and may be responsible for altered gait mechanics.     

Exercise-induced abdominal muscle fatigue in healthy humans.

The abdominal muscles have been shown to fatigue in response to voluntary isocapnic hyperpnea using direct nerve stimulation techniques. We investigated whether the abdominal muscles fatigue in response to dynamic lower limb exercise using such techniques. Eleven male subjects [peak oxygen uptake (VO2 peak) = 50.0 +/- 1.9 (SE) ml.kg(-1).min(-1)] cycled at >90% VO2 peak to exhaustion (14.2 +/- 4.2 min). Abdominal muscle function was assessed before and up to 30 min after exercise by measuring the changes in gastric pressure (Pga) after the nerve roots supplying the abdominal muscles were magnetically stimulated at 1-25 Hz. Immediately after exercise there was a decrease in Pga at all stimulation frequencies (mean -25 +/- 4%; P < 0.001) that persisted up to 30 min postexercise (-12 +/- 4%; P = 0.001). These reductions were unlikely due to changes in membrane excitability because amplitude, duration, and area of the rectus abdominis M wave were unaffected. Declines in the Pga response to maximal voluntary expiratory efforts occurred after exercise (158 +/- 13 before vs. 145 +/- 10 cmH2O after exercise; P = 0.005). Voluntary activation, assessed using twitch interpolation, did not change (67 +/- 6 before vs. 64 +/- 2% after exercise; P = 0.20), and electromyographic activity of the rectus abdominis and external oblique increased during these volitional maneuvers. These data provide new evidence that the abdominal muscles fatigue after sustained, high-intensity exercise and that the fatigue is primarily due to peripheral mechanisms.     

Comparison of oxidative stress and antioxidant capacity before and after running exercises in both sexes

Background: It has been difficult to determine, from the published literature, whether men or women have higher levels of exercise-induced oxidative stress.Objective: The aim of this study was to compare variations between the sexes in lipid hydroperoxide (LPO), superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and lactate dehydrogenase (LDH) after 3 different running exercises performed at the same speed.Methods: Eligible participants were healthy university students of both sexes. The participants performed running exercise tests at distances of 800, 1500, and 3000 m at a speed of 10 km/h. Blood samples were taken from the participants just before and immediately after the running activities to determine LPO, SOD, CAT, GR, and LDH, and these measures were compared both before and after exercise and between the sexes.Results: A total of 17 young and healthy, but not physically trained, students (n = 8 men; mean age, 22.00 years; n = 9 women; mean age, 21.78 years) participated in this study. Height, weight, and maximum oxygen consumption values were significantly higher in men than in women (P = 0.01). Significant gender effects were found in LPO levels at 3000 m (F = 5.51; P = 0.03) and in SOD activity at 800 m (F = 7.92; P = 0.01) and 3000 m (F = 6.05; P = 0.03). CAT activity also differed between the sexes at 800 m (F = 15.67; P = 0.01) and 1500 m (F = 6.55; P = 0.02). However, no significant gender-time interaction effect was observed for any measurement at the 800-, 1500-, and 3000-m distances.Conclusions: Changes in LPO, SOD, and CAT activities at different running distances were not different between men and women over time because of a nonsignificant gender-time interaction. With regard to changes in oxidative stress, men and women had similar responses to exercise at the same absolute workload, despite significant differences in physical characteristics.     

Lower extremity muscle activation during horizontal and uphill running

Sloniger, Mark A., Kirk J. Cureton, Barry M. Prior, andEllen M. Evans. Lower extremity muscle activationduring horizontal and uphill running. J. Appl.Physiol. 83(6): 2073-2079, 1997.To provide more comprehensive information on theextent and pattern of muscle activation during running, we determinedlower extremity muscle activation by using exercise-induced contrastshifts in magnetic resonance (MR) images during horizontal and uphillhigh-intensity (115% of peak oxygen uptake) running to exhaustion(2.0-3.9 min) in 12 young women. The mean percentage of musclevolume activated in the right lower extremity was significantly(P <0.05) greater during uphill (73 ± 7%) than during horizontal (67 ± 8%) running. Thepercentage of 13 individual muscles or groups activated varied from 41 to 90% during horizontal running and from 44 to 83% during uphillrunning. During horizontal running, the muscles or groups mostactivated were the adductors (90 ± 5%), semitendinosus (86 ± 13%), gracilis (76 ± 20%), biceps femoris (76 ± 12%), andsemimembranosus (75 ± 12%). During uphill running, the musclesmost activated were the adductors (83 ± 8%), biceps femoris (79 ± 7%), gluteal group (79 ± 11%), gastrocnemius (76 ± 15%), and vastus group (75 ± 13%). Compared with horizontalrunning, uphill running required considerably greater activation of thevastus group (23%) and soleus (14%) and less activation of the rectusfemoris (29%), gracilis (18%), and semitendinosus (17%). We concludethat during high-intensity horizontal and uphill running to exhaustion,lasting 2-3 min, muscles of the lower extremity are not maximallyactivated, suggesting there is a limit to the extent to whichadditional muscle mass recruitment can be utilized to meet the demandfor force and energy. Greater total muscle activation during exhaustive uphill than during horizontal running is achieved through an altered pattern of muscle activation that involves increased use of some muscles and less use of others.