Hormonal responses to high- and moderate-intensity strength exercise

The hormonal responses of nine male, strength athletes to strength exercise were examined. The athletes performed one moderate- and one high-intensity strength exercise workout. In the high-intensity workout, the load was 100% of each subject's three-repetition maximum (3-RM) for squats and front squats, and 100% of each subject's six-repetition maximum (6-RM) for leg extensions. In the moderate-intensity workout, the load was 70% of the high-intensity protocol. Rest periods between sets were 4–6 min for both workouts. Blood samples were taken before, 30 min into, and every 15 min for the 1st h after exercise, and then 3, 7, 11, 22 and 33 h after exercise, thus allowing examination of both the acute and prolonged hormonal responses. Blood samples were analyzed for testosterone, luteinizing hormone (LH), follicle stimulating hormone (FSH), cortisol, adrenocorticotrophic hormone (ACTH), growth hormone (GH), insulin-like growth factor (IGF-1), insulin, sex hormone binding globulin, creatine kinase, total protein, glucose and lactate. The acute responses of testosterone and cortisol were greater during the high-intensity protocol as compared to the moderate-intensity protocol. The cortisol response was associated with an increase in ACTH concentration. LH and FSH showed no response to either protocol. Acute GH responses were not different between protocols. There were great inter-individual differences in acute GH responses to both protocols. There were no significant differences between protocols with regard to prolonged responses for any hormone. In both trials, IGF-1 concentrations were significantly lower at 0800 hours the morning after exercise as compared to concentrations found at 0800 hours the morning before exercise. The mechanisms responsible for reducing IGF-1 concentration in these trials are unclear, and it is not known if this reduction observed 22 hours after exercise is of physiological significance. Accepted: 13 December 1999     

Short-term exercise training improves diaphragm antioxidant capacity and endurance

These experiments tested the hypothesis that short-term endurance exercise training would rapidly improve (within 5 days) the diaphragm oxidative/antioxidant capacity and protect the diaphragm against contraction-induced oxidative stress. To test this postulate, male Sprague-Dawley rats (6 weeks old) ran on a motorized treadmill for 5 consecutive days (40–60 min · day⁻¹) at approximately 65% maximal oxygen uptake. Costal diaphragm strips were excised from both sedentary control (CON, n=14) and trained (TR, n=13) animals 24 h after the last exercise session, for measurement of in vitro contraction properties and selected biochemical parameters of oxidative/antioxidant capacity. Training did not alter diaphragm force-frequency characteristics over a full range of submaximal and maximal stimulation frequencies (P > 0.05). In contrast, training improved diaphragm resistance to fatigue as contraction forces were better-maintained by the diaphragms of the TR animals during a submaximal 60-min fatigue protocol (P < 0.05). Following the fatigue protocol, diaphragm strips from the TR animals contained 30% lower concentrations of lipid hydroperoxides compared to CON (P < 0.05). Biochemical analysis revealed that exercise training increased diaphragm oxidative and antioxidant capacity (citrate synthase activity +18%, catalase activity +24%, total superoxide dismutase activity +20%, glutathione concentration +10%) (P < 0.05). These data indicate that short-term exercise training can rapidly elevate oxidative capacity as well as enzymatic and non-enzymatic antioxidant defenses in the diaphragm. Furthermore, this up-regulation in antioxidant defenses would be accompanied by a reduction in contraction-induced lipid peroxidation and an increased fatigue resistance. Accepted: 6 August 1999     

Muscle activation of the knee extensors following high intensity endurance exercise in cyclists

This study was conducted to assess the effects in trained cyclists of exhausting endurance cycle exercise (CE) on maximal isometric force production, surface electromyogram (EMG) and activation deficit (AD) of the knee extensors. Ten male subjects made four isometric maximal voluntary contractions (MVC) of the knee extensor muscles immediately prior (pre), 10 min after (post) and 6 h after completion of CE. The CE consisted of 30 min of exercise on a stationary cycle ergometer at an intensity corresponding to 80% of maximal oxygen uptake (V˙O_2max) followed by four × 60-s periods at 120% of V˙O_2max. Two MVC were performed with recording of surface EMG from the knee extensors, whilst an additional two MVC were completed with percutaneous electrical muscle stimulation (EMS; 25 pulses at 100 Hz with the maximal tolerable current) superimposed over the maximal voluntary contraction force (MVF) but without EMG (to avoid interference). The MVF, integrated EMG (iEMG), and AD [calculated as the difference between MVF and the electrically stimulated force (ESF) during the EMS contractions] were statistically analysed. The MVF was significantly reduced (P < 0.05) post and 6-h post compared to pre-CE level. The iEMG was significantly reduced (P < 0.05) post and 6 h post CE. The ESF was also reduced, whilst AD was significantly increased (P < 0.05) post and 6-h post CE compared to the pre CE. These results suggest that the level of exercise stress administered in this study was sufficient to impair the central and peripheral mechanisms of force generation in knee extensors for a period of 6-h. Athletes engaged in concurrent training (strength and endurance) should consider this effect in exercise programming. Accepted: 22 September 1999     

Neuromuscular adaptation during prolonged strength training, detraining and re-strength-training in middle-aged and elderly people

Effects of a 24-week strength training performed twice weekly (24 ST) (combined with explosive exercises) followed by either a 3-week detraining (3 DT) and a 21-week re-strength-training (21 RST) (experiment A) or by a 24-week detraining (24 DT) (experiment B) on neural activation of the agonist and antagonist leg extensors, muscle cross-sectional area (CSA) of the quadriceps femoris, maximal isometric and one repetition maximum (1-RM) strength and jumping (J) and walking (W) performances were examined. A group of middle-aged (M, 37–44 years, n=12) and elderly (E, 62–77, n=10) and another group of M (35–45, n=7) and E (63–78, n=7) served as subjects. In experiment A, the 1-RM increased substantially during 24 ST in M (27%, P < 0.001) and E (29%, P < 0.001) and in experiment B in M (29%, P < 0.001) and E (23%, P < 0.01). During 21 RST the 1-RM was increased by 5% at week 48 (P < 0.01) in M and 3% at week 41 in E (n.s., but P < 0.05 at week 34). In experiment A the integrated electromyogram (IEMG) of the vastus muscles in the 1-RM increased during 24 ST in both M (P < 0.05) and E (P < 0.001) and during 21 RST in M for the right (P < 0.05) and in E for both legs (P < 0.05). The biceps femoris co-activation during the 1-RM leg extension decreased during the first 8-week training in M (from 29 ± 5% to 25 ± 3%, n.s.) and especially in E (from 41 ± 11% to 32 ± 9%, P < 0.05). The CSA increased by 7% in M (P < 0.05) and by 7% in E (P < 0.001), and by 7% (n.s.) in M and by 3% in E (n.s.) during 24 ST periods. Increases of 18% (P < 0.001) and 12% (P < 0.05) in M and 22% (P < 0.001) and 26% (P < 0.05) in E occurred in J. W speed increased (P < 0.05) in both age groups. The only decrease during 3 DT was in maximal isometric force in M by 6% (P < 0.05) and by 4% (n.s.) in E. During 24 DT the CSA decreased in both age groups (P < 0.01), the 1-RM decreased by 6% (P < 0.05) in M and by 4% (P < 0.05) in E and isometric force by 12% (P < 0.001) in M and by 9% (P < 0.05) in E, respectively, while J and W remained unaltered. The strength gains were accompanied by increased maximal voluntary neural activation of the agonists in both age groups with reduced antagonist co-activation in the elderly during the initial training phases. Neural adaptation seemed to play a greater role than muscle hypertrophy. Short-term detraining led to only minor changes, while prolonged detraining resulted in muscle atrophy and decreased voluntary strength, but explosive jumping and walking actions in both age groups appeared to remain elevated for quite a long time by compensatory types of physical activities when performed on a regular basis. Accepted: 2 May 2000     

Cytokines and cell adhesion molecules associated with high-intensity eccentric exercise

Unaccustomed, eccentrically biased exercise induces trauma to muscle and/or connective tissue. Tissue damage activates an acute inflammatory response. Inflammation requires the effective interaction of different physiological and biological systems. Much of this is coordinated by the de novo synthesis of families of protein molecules, cytokines. The purpose of the present paper was to determine changes in blood levels of various cytokines in response to exercise-induced muscle damage that was effected using high-intensity eccentric exercise. Six healthy, untrained, college-age male subjects were required to perform the eccentric phase of a bench press and a leg curl (4 sets, 12 repetitions/set) at an intensity equivalent to 100% of their previously determined one-repetition maximum. Samples of blood were drawn at the following times: before exercise and 1.5, 6, 12, 24, 48, 72, 96, 120, and 144 h after exercise. These samples were analyzed for interleukins (IL): IL-lβ, IL-6, and IL-10; tumor necrosis factor-α; colony stimulating factors (CSF): granulocyte-CSF, macrophage-CSF, and GM-CSF; for cell adhesion molecules (CAM): P- and E-selectin, and intercellular cell adhesion molecule (ICAM-1), and vascular cell adhesion molecule (VCAM-1). Results were analyzed using a repeated-measures analysis of variance (P=0.05). Compared to baseline values, IL-1β was reduced (P=0.03) at 6, 24, and 96–144 h after exercise; IL-6 was elevated (P=0.01) at 12, 24, and 72 h after exercise; IL-10 was elevated (P=0.009) between 72 and 144 h after exercise; M-CSF was elevated (P=0.005) at 12 and 48–144 h after exercise; and P-selectin was reduced (P=0.01) between 24 and 144 h after exercise. It is concluded that when high-intensity eccentric exercise is compared to strenuous endurance exercise, post-exercise changes in cytokines do occur, but they are generally of a smaller magnitude, and occur at a later time period after the termination of exercise. Accepted: 28 December 1999     

Alterations in the expression and activity of creatine kinase-M and mitochondrial creatine kinase subunits in skeletal muscle following prolonged intense exercise in rats

Creatine kinase (CK) isoenzymes are important structural and energy metabolism components in skeletal muscle. In this study, CK isoenzyme alterations were examined in male rats, with an 8% body mass weight attached to their tail. The rats were either forced to swim for 5 h (5S, n = 51), or were pre-trained for 8 days and then forced to swim for 5 h (T5S, n = 48). Rats were sacrificed either immediately (0 h PS), 3 h (3 h PS), or 48 h post-swimming (48 h PS). Serum CK was increased significantly (P < 0.01) 6.2- and 2.0-fold at 0 h PS following the 5S and T5S protocols, respectively. However, training (T5S protocol) significantly (P < 0.01) decreased CK release. Soleus and white gastrocnemius (WG) CK activity was significantly decreased following the 5S protocol (P < 0.05), but not following the T5S protocol. The CK-M activity of the soleus muscle was significantly (P < 0.05) decreased at 0 h PS following both the 5S and T5S protocols, and returned to control values at 3 h PS. The CK-M activity of the WG was significantly (P < 0.05) decreased at 0 h PS following the 5S protocol. Sarcomeric mitochondrial CK (sCK-Mit) was decreased significantly (P < 0.01) at 0 h PS (20%), 3 h PS (14%), 24 h PS (22%), and 48 h PS (15%) following the 5S protocol. However, sCK-Mit was decreased significantly (P < 0.01) only at 0 h PS (7%) following the T5S. The results of this study demonstrate that prolonged intense exercise causes a loss of skeletal muscle CK-M and sCK-Mit activity and that training prior to the prolonged intense exercise attenuates the exercise-induced CK-M and sCK-Mit loss in both red and white skeletal muscles. Accepted: 18 July 1999     

Force/velocity and power/velocity relationships in squat exercise

The purpose of this study was to describe the force/velocity and power/velocity relationships obtained during squat exercise. The maximal force (F ₀) was extrapolated from the force/velocity relationship and compared to the isometric force directly measured with the aid of a force platform placed under the subject's feet. Fifteen international downhill skiers [mean (SD) age 22.4 (2.6) years, height 178 (6.34) cm and body mass 81.3 (7.70) kg] performed maximal dynamic and isometric squat exercises on a guided barbell. The dynamic squats were performed with masses ranging from 60 to 180 kg, which were placed on the shoulders. The force produced during the squat exercise was linearly related to the velocity in each subject (r ²=0.83–0.98, P < 0.05–0.0001). The extrapolated F ₀ was 23% higher than the measured isometric force (P < 0.001), and the two measurements were not correlated. This may be attributed to the position of the subject, since the isometric force was obtained at a constant angle (90° of knee flexion), whereas the dynamic forces were measured through a range of movements (from 90° to 180°). The power/velocity relationship was parabolic in shape for each subject (r ²=0.94–0.99, P < 0.01–0.0001). However, the curve obtained exhibited only an ascending part. The highest power was produced against the lightest load (i.e., 60 kg). The maximal power (W˙ _max ) and optimal velocity were never reached. The failure to observe the descending part of the power/velocity curve may be attributed to the upper limitation of the velocities studied. Nevertheless, the extrapolation of W˙ _max from the power/velocity equation showed that it would be reached for a load close to body mass, or even under unloaded conditions. Accepted: 19 September 2000     

Plasma catecholamine responses and neural adaptation during short-term resistance training

Low exercise-induced plasma adrenaline (A) responses have been reported in resistance-trained individuals. In the study reported here, we investigated the interaction between strength gain and neural adaptation of the muscles, and the plasma A response in eight healthy men during a short-term resistance-training period. The subjects performed 5 resistance exercises (E1–E5), consisting of 6 sets of 12 bilateral leg extensions performed at a 50% load, and with 2 days rest in between. Average electromyographic (EMG) signal amplitude was recorded before and after the exercises, from the knee extensor muscles in isometric maximal voluntary contraction (MVC) as well as during the exercises (aEMG_max and aEMG_exerc, respectively). Total oxygen consumed during the exercises (V˙O_2tot) was also measured. All of the exercises were exhaustive and caused significant decreases in MVC (34–36%, P < 0.001). As expected, the concentric one-repetition maximum (1-RM), MVC and aEMG_max were all higher before the last exercise (E5) than before the first exercise (E1; 7, 9 and 19%, respectively, P < 0.05). In addition, in E5 the aEMG_exerc:load and V˙O_2tot:load ratios were lower than in E1 (−5 and −14%, P < 0.05), indicating enhanced efficiency of the muscle contractions, However, the post-exercise plasma noradrenaline (NA) and A were not different in these two exercises [mean (SD) 10.2 (3.8) nmol · l⁻¹ vs 11.3 (6.0) nmol · l⁻¹, ns, and 1.2 (1.0) nmol · l⁻¹ vs 1.9 (1.1) nmol · l⁻¹, ns, respectively]. However, although NA increased similarly in every exercise (P < 0.01), the increase in A reached the level of statistical significance only in E1 (P < 0.05). The post-exercise A was also already lower in E2 [0.7 (0.7) nmol · l⁻¹, P < 0.05) than in E1, despite the higher post-exercise blood lactate concentration than in the other exercises [9.4 (1.1) mmol · l⁻¹, P < 0.05]. Thus, the results suggest that the observed attenuation in the A response can not be explained by reduced exercise-induced strain due to the strength gain and neural adaptation of the muscles. Correlation analysis actually revealed that those individuals who had the highest strength gain during the training period even tended to have an increased post-exercise A concentration in the last exercise as compared to first one (r=0.76, P < 0.05). Accepted: 10 February 2000     

Effects of knee joint angles and fatigue on the neuromuscular control of vastus medialis oblique and vastus lateralis muscle in humans

The effects of different knee joint angles and fatigue on the neuromuscular control of the vastus medialis oblique (VMO) and vastus lateralis (VL) muscles were investigated in 17 (11 men, 6 women) young subjects. The electromyogram (EMG) activities and the force generation capacities were monitored before and after a fatigue protocol at three different knee joint angles, 90°, 150°, 175° of knee extension, on three occasions. In response to randomly triggered light signals, the subjects performed three isometric maximal voluntary contraction (IMVC) that lasted for 4 to 8 s. This was then followed by the fatigue protocol which consisted of six bursts of contractions fixed at 30 s on and 10 s off. Immediately after the exercise to fatigue, the subjects performed another three IMVC in response to the light signals. Repeated measures ANOVA were performed to examine the effects of fatigue at these three positions on the electromechanical delay (EMD), median frequency (f _med), peak force (F _peak) and root mean square (rms)-EMG:F _peak quotient of VMO and VL. The results revealed a significant effect of the three knee joint angles on the EMD before the fatigue (P < 0.05). The fatigue protocol induced a significant decrease in F _peak at all the three positions (P < 0.01). However, the fatigue induced a significant decrease of f _med at only 90° and 150° of knee extension (P < 0.01). This occurred in parallel with the lengthening of EMD at these two joint angles (P < 0.01 and P < 0.05). The effects of fatigue on the f _med and EMD were not significant between VMO and VL at all three angles. The insignificant difference in f _med and EMD between VMO and VL at the three knee positions before and after fatigue indicated that no preferential onset activation between VMO and VL had occurred. Accepted: 1 September 2000     

Do knee injuries have long-term consequences for isometric and dynamic muscle strength?

To ascertain whether decrements in knee extensor muscle strength persist years after a traumatic ligamentous or meniscal knee injury, with reference to (1) the type of muscle activity, (2) the dominance of injury, and (3) the time since injury, 36 subjects with previous unilateral knee injuries were assessed. Peak voluntary quadriceps muscle strength was measured using the KinCom 500H dynamometer during isometric, concentric (30°·s^–1 and 120°·s^–1) and eccentric contractions (30·s^–1), and the findings for each type of contraction were compared. Significant differences in quadriceps muscle strength were seen between (1) the injured and uninjured limbs during maximal voluntary isometric (P=0.0003), concentric (P<0.0001) and eccentric (P<0.0001) contractions, and (2) the isometric and concentric decrements (P=0.004), and the isometric and eccentric decrements (P=0.012) within the same injured limb. The decrements in eccentric strength were significantly greater if they affected the dominant rather than the non-dominant limb (P=0.0186). No relationship was seen between the time since injury and the degree of isometric or dynamic decrement. Deficits in quadriceps muscle strength remained for a long time after traumatic knee injury, with exercise levels rarely returning to the previously uninjured state. The degree of decrement in muscle strength was dependent upon the type of muscle activity, with concentric and eccentric activity showing greater decrements than those seen with isometric activity. Deficits in the type of activity varied widely in the same individual, and eccentric decrements were significantly worse following dominant knee injuries. Possible explanations for these findings and the implications for rehabilitation following knee injury are discussed. Electronic Publication     

Effects of moderate dietary manipulation on intermittent exercise performance and metabolism in women

The aim of the current study was to examine the effect of a moderate alteration in pre-exercise diet composition on the performance of, and metabolic response to, intermittent treadmill exercise in a group of normally menstruating females. Eight recreationally active women performed two intermittent, incremental exercise trials, one preceded by 2 days of a high [61 (1)%] carbohydrate (CHO) diet and the other by 2 days of a low [31 (1)%] CHO diet. Oxygen uptake (VO₂) was measured during, and blood samples were obtained immediately after, each bout for the determination of blood lactate, glucose, glycerol, plasma free fatty acids and plasma ammonia. Performance, as assessed by time to exhaustion in the final bout, was found to be similar whether preceded by a high- or low-CHO diet [median (range): 28.0 (18–54) s, 29 (18–54) s, respectively]. No significant between trial differences were found in VO₂, heart rate, or any of the blood metabolites. The results of the current study indicate that moderate alterations of pre-exercise diet do not affect intermittent, high-intensity exercise performance in women, despite some evidence of an alteration in the pattern of the metabolic response to exercise. Accepted: 7 September 1999     

Effect of creatine feeding on maximal exercise performance in vegetarians

The effect of creatine supplementation on exercise performance in vegetarians was examined. Creatine was ingested for 1 week by a group of vegetarians (VC) and meat-eaters (MC); a control group of meat-eaters was fed only glucose (MG). Exercise performance during three, 20-s maximal cycling tests (modified Wingate anaerobic test, WAnT) was determined before and after creatine supplementation. Blood samples were also drawn before and after exercise prior to and after supplementation. Basal plasma creatine (after an overnight fast) averaged (SE) 11 (2) μM in VC, and 24 (2) and 23 (7) μM in MG and MC, respectively (P < 0.05 for VC vs meat-eaters). These findings were expected, since most of the body's exogenous creatine source is meat. There was no significant difference in any other parameter between groups prior to supplementation. Creatine feedings significantly increased body mass (≅1 kg) and mean power output during the WAnTs (≅5%) to a similar extent in the VC and MC groups (P < 0.05–0.001). These parameters were not affected by supplementation in the MG group. Peak power output was also significantly increased by supplementation in MC (≅5%, P < 0.05), but not in VC. It is concluded that vegetarians and meat-eaters respond to creatine feedings with similar increases in mean power output during short-term, maximal exercise. Accepted: 24 March 2000     

Force recovery after eccentric exercise in males and females

In this study we investigated force loss and recovery after eccentric exercise, and further characterized profound losses in muscle function (n=192 subjects – 98 males, 94 females; population A). Maximal voluntary contractile force (MVC) was assessed before, immediately after, and at 36 and 132 h after eccentric exercise. Two groups were then established (A₁ and A₂). Group A₁ demonstrated a >70% reduction in MVC immediately after exercise, but were recovering at 132 h after exercise. These subjects performed a follow-up MVC 26 days later (n=32). Group A₂ demonstrated a >70% reduction in MVC immediately post-exercise, but still exhibited a >65% reduction in force at 132 h post-exercise; these subjects also performed a follow-up MVC every 7 days until full recovery was established (n=9). In population A, there was a 57% reduction in MVC immediately post-exercise and a 67% recovery by 132 h post-exercise (P < 0.01), with no significant gender differences (P > 0.05). In group A₁, although more females (two-thirds) showed large force losses after exercise, these females demonstrated greater %MVC recovery at 132 h post-exercise (59% vs 44%) and at 26 days post-exercise (93% vs 81%) compared to the males. In group A₂, MVC recovery occurred between 33 and 47 days post-exercise. In conclusion, 21% of all subjects showed a delayed recovery in MVC after high-force eccentric exercise. Although there were no significant gender differences in force loss, a disproportionately larger number of females demonstrated force reductions of >70%. However, their recovery of force was more rapid than that observed for the males who also demonstrated a >70% force loss. Accepted: 2 October 2000     

Effects of laboratory versus field exercise on leukocyte subsets and cell adhesion molecule expression in children

In adults, exercise is a powerful and natural stimulator of immune cells and adhesion molecules. Far less is known about these exercise responses during childhood and whether or not exercise in real-life activities of healthy children might influence immune responses. We compared laboratory exercise (10×2 min periods of heavy, constant intensity, cycle ergometer exercise with 1 min rests between exercise in nine subjects, aged 9–15 years) with field exercise (90 min soccer practice in nine different subjects, aged 9–11 years). Blood was sampled before both protocols, 5 min after the 30 min laboratory protocol, and 10–15 min after the 90 min field protocol. Both field and laboratory exercise protocols led to significant (P<0.05) increases in granulocytes, monocytes, and all lymphocyte subpopulations. The mean (SEM) increases were similar for the two protocols except for the significantly greater increase in laboratory compared with field protocols for natural killer cells [142 (39)% vs 12 (16)%, P<0.001] and monocytes [64 (22)% vs 32 (19)%, P<0.001]. Both protocols significantly influenced adhesion molecules (such as CD54) which have not been previously studied in children. However, the adhesion molecule CD8⁺CD62L^– increased to a significantly (P<0.001) greater extent in the laboratory [101 (25)%] versus field [34 (25)%] protocol. Finally, the density of CD62L on lymphocytes significantly decreased with laboratory exercise but showed no change in the field protocol [–20 (3)% vs –3 (3)%, P<0.001]. The rapid and substantial immune response in both laboratory and field protocols suggests that exercise stimulation of the immune system occurs commonly in the real lives of children and may play a role in their overall immune status. Electronic Publication     

The effect of diet on vitamin E intake and oxidative stress in response to acute exercise in female athletes

Vitamin E is the major lipid-soluble antioxidant found in foods, and its bioavailability is affected by the presence of dietary fats. Athletes often consume low-fat diets and may be more susceptible to the oxidative stress produced by exercise due to the low availability of vitamin E. In this study, the effects of a low-fat diet on vitamin E intake and oxidative stress markers were assessed in collegiate female rowers. All subjects habitually consumed either a low-fat (LF; <40 g fat · day⁻¹) or a high-fat (HF; >60 g fat · day⁻¹) diet. Subjects ran downhill for 45 min at 75% of their age-predicted maximal heart rate. Blood samples were collected immediately pre- and post-exercise, and at 6, 24, and 48 h post-exercise. Subjects in the LF group consumed significantly less vitamin E (2.9 mg vitamin E · day⁻¹) than advised by the Recommended Dietary Allowance (RDA; 8.0 mg vitamin E · day⁻¹) and than those in the HF group (9.8 mg vitamin E · day⁻¹; P < 0.05). Plasma concentrations of vitamin E, malondialdehyde, and conjugated dienes were not significantly different between LF and HF before or after exercise. Creatine kinase became significantly elevated above baseline at 6 h and 24 h post-exercise in both groups (P < 0.05). We can conclude from these data that although the subjects in the LF group were not consuming the recommended amount of vitamin E in their diets, their vitamin E intake appears to be sufficient to protect against the oxidative stress produced by this moderate-intensity exercise. Accepted: 28 April 2000     

Combined effects of low-intensity blood flow restriction training and high-intensity resistance training on muscle strength and size

We investigated the combined effect of low-intensity blood flow restriction and high-intensity resistance training on muscle adaptation. Forty young men (aged 22–32 years) were randomly divided into four groups of ten subjects each: high-intensity resistance training (HI-RT, 75% of one repetition maximum [1-RM]), low-intensity resistance training with blood flow restriction (LI-BFR, 30% 1-RM), combined HI-RT and LI-BFR (CB-RT, twice-weekly LI-BFR and once-weekly HI-RT), and nontraining control (CON). Three training groups performed bench press exercises 3 days/week for 6 weeks. During LI-BFR training sessions, subjects wore pressure cuffs on both arms that were inflated to 100–160 mmHg. Increases in 1-RM were similar in the HI-RT (19.9%) and CB-RT (15.3%) groups and lower in the LI-BFR group (8.7%, p < 0.05). Maximal isometric elbow extension (MVC) increased in the HI-RT (11.3%) and CB-RT (6.6%) groups; there was no change in the LI-BFR group (−0.2%). The cross-sectional area (CSA) of the triceps brachii (TB) increased (p < 0.05) in the HI-RT (8.6%), CB-RT (7.2%), and LI-BFR (4.4%) groups. The change in relative isometric strength (MVC divided by TB CSA) was greater (p < 0.05) in the HI-RT group (3.3%) than in the LI-BFR (−3.5%) and CON (−0.1%) groups. Following training, relative dynamic strength (1-RM divided by TB CSA) was increased (p < 0.05) by 10.5% in the HI-RT group and 6.7% in the CB-RT group. None of the variables in the CON group changed. Our results show that low-intensity resistance training with BFR-induced functional muscle adaptations is improved by combining it with HI-RT.     

Effect of exercise-induced muscle damage on ventilatory and perceived exertion responses to moderate and severe intensity cycle exercise

This study examined the effect of exercise-induced muscle damage (EIMD) on ventilatory and perceived exertion responses to cycle exercise. Ten healthy, physically active men cycled for 6 min at moderate intensity and to exhaustion at severe intensity before and 48 h after eccentric exercise (100 squats with a load corresponding to 70% of body mass). Changes in ventilation and ratings of perceived exertion (RPE) were calculated for each individual and expressed against time (moderate and severe exercise) and as a percentage of time to exhaustion (severe exercise). Ventilation increased during moderate exercise at 48 h ( [(V)\dot]_\textE \dot{V}_{\text{E}} ; 34.5 ± 5.0 to 36.3 ± 3.8 l min⁻¹, P < 0.05) but increases in RPE were not significant. During severe exercise at 48 h, time to exhaustion (TTE) was reduced and [(V)\dot]_\textE \dot{V}_{\text{E}} (87.1 ± 14.1 to 93.8 ± 11.7 l min⁻¹) and RPE (15.5 ± 1.3 to 16.1 ± 1.4) were elevated (P < 0.05). When expressed as a percentage of TTE, the differences in ventilation and RPE values disappeared. Findings indicate that the augmented ventilatory response to cycle exercise following EIMD may be an important cue in informing effort perception during high-intensity exercise but not during moderate-intensity exercise.     

Human hip and knee torque accommodations to anterior cruciate ligament dysfunction

It has been postulated that the adaptations of lower extremity function exhibited by anterior cruciate ligament (ACL) deficient and post-ACL surgical patients represent early accommodations to the loss of ACL function after injury so that excessive anterior displacement of the tibia is prevented. Prior studies have suggested that compensation patterns in ACL deficient and post-ACL surgical subjects may affect joint moments of the knee as well as the hip. However, the variance in knee and hip forces between ACL deficient, post-surgical ACL and uninjured groups has not been clearly elucidated. The purpose of this study was to assess hip:knee extensor torque ratios relative to anterior tibia shear in pre-surgical-ACL deficient, post-surgical and uninjured subjects. Measurements of hip and knee joint moments and anterior tibia shear were recorded from 45 injured and uninjured subjects (21 men, 24 women) during lower extremity, variable resistance exercise. Anterior tibia shear was computed by decomposing joint moments and reaction forces according to a model derived from cadaver knee dissections and radiography, in combination, to estimate the tibio-femoral compressive and shear forces generated by the patellar tendon at various angles throughout the knee joint range. Three groups of subjects were studied: recently injured ACL deficient pre-surgical subjects who were scheduled for immediate surgery (PRE; n=15); post-surgical subjects who had undergone ACL reconstructive surgery at least 1 year prior to testing (POST; n=15); and uninjured controls (CON; n=15). All PRE and POST subjects had a normal contralateral limb. Tests were conducted under six conditions: 1 and 1.5 Hz cadence and maximal speed at 33% and 50% one repetition maximum resistance. The results revealed that the hip:knee ratios were significantly greater for the post-ACL surgical group than the PRE and CON groups (P < 0.01; P < 0.03). There were significant negative correlations between the hip extensor:knee extensor torque ratios and maximal anterior tibia shear. across all groups. The hip:knee extensor torque ratio increased with decreased anterior tibia shear in all groups with significant correlations ranging from −0.55 to −0.88 (P < 0.01) for the injured limbs of PRE and POST groups, and −0.64 to −0.78; (P < 0.01) for the CON group. The highest overall correlations were found for the post-surgical subjects. The results revealed that anterior tibia shear declined significantly with speed (P < 0.01) in all groups. However, the converse was true for the hip:knee extensor torque ratio across speeds. The ratio increased significantly with speed (P < 0.001) for all groups at the 33% and 50% resistances. The results suggest (1) that post-ACL surgical subjects appear to accommodate to ACL substitution by using hip extensors to a significantly greater extent than the uninjured controls in closed-chain lower extremity exercise; (2) that the hip:knee extensor torque ratio is significantly related to the magnitude of anterior tibia shear; and (3) that the anterior tibia shear is significantly reduced as speed increases in closed-chain lower extremity exercise. Accepted: 30 April 2000     

Strenuous endurance training in humans reduces oxidative stress following exhausting exercise

The aim of this study was to evaluate whether high-intensity endurance training would alleviate exercise-induced oxidative stress. Nine untrained male subjects (aged 19–21 years) participated in a 12-week training programme, and performed an acute period of exhausting exercise on a cycle ergometer before and after training. The training programme consisted of running at 80% maximal exercise heart rate for 60 min · day⁻¹, 5 days · week⁻¹ for 12 weeks. Blood samples were collected at rest and immediately after exhausting exercise for measurements of indices of oxidative stress, and antioxidant enzyme activities [superoxide dismutase (SOD), glutathione peroxidase (GPX), and catalase (CAT)] in the erythrocytes. Maximal oxygen uptake (V˙O_2max) increased significantly (P < 0.001) after training, indicating an improvement in aerobic capacity. A period of exhausting exercise caused an increase (P < 0.01) in the ability to produce neutrophil superoxide anion (O₂ ^•−) both before and after endurance training, but the magnitude of the increase was smaller after training (P < 0.05). There was a significant increase in lipid peroxidation in the erythrocyte membrane, but not in oxidative protein, after exhausting exercise, however training attenuated this effect. At rest, SOD and GPX activities were increased after training. However, there was no evidence that exhausting exercise enhanced the levels of any antioxidant enzyme activity. The CAT activity was unchanged either by training or by exhausting exercise. These results indicate that high-intensity endurance training can elevate antioxidant enzyme activities in erythrocytes, and decrease neutrophil O₂ ^•− production in response to exhausting exercise. Furthermore, this up-regulation in antioxidant defences was accompanied by a reduction in exercise-induced lipid peroxidation in erythrocyte membrane. Accepted: 26 September 2000