Characterization of a rabbit antihuman mechano growth factor (MGF) polyclonal antibody against the last 24 amino acids of the E domain

The human insulin-like growth factor-1 (IGF-1) gene gives rise to multiple, heterogeneous mRNA transcripts by alternative splicing, thus producing different IGF-1 isoforms. The mechano growth factor (MGF) is an IGF-1 isoform that was found to be markedly up-regulated in exercised or damaged muscle. The specific E domain of the MGF splice variant may act as an independent growth factor. The aim of the present study was to characterize a rabbit antihuman MGF polyclonal antibody. New-Zealand rabbits were immunized by injections of a purified synthetic peptide corresponding to the last 24 amino acids of the human C-terminal of the MGF E domain. Western blotting and immunohistochemical techniques were used to characterize the specificity of the polyclonal anti-MGF antiserum. The anti-MGF antiserum was found to recognize the MGF E-peptide and not the common part of the IGF-1 isoforms, i.e. the mature IGF-1 peptide. Furthermore, it specifically bound to the MGF protein in human skeletal and in rat cardiac muscle, apparently due to the considerable homology between the human and rat MGF E-peptide sequences. Immunostaining analysis showed that this polyclonal anti-MGF antibody was able to detect MGF in human muscle and in rat cardiomyocytes and vessels' smooth muscle cells. We conclude that this rabbit polyclonal anti-human/rat MGF antibody could become a valuable tool in the study of IGF-1 isoforms in human and rat tissues.

Cardiorespiratory and metabolic responses to a simulated synchronized swimming routine in senior (>18 years) and comen (13-15 years) national level athletes

AIM

This study examined the ventilatory responses and blood lactate concentration after a simulated synchronized swimming routine of athletes of two different age categories.

METHODS

Sixteen trained female synchronized swimmers, 8 competing at the comen category (age: 13.8+/-0.2 years) and 8 competing at the senior category (age: 22.6+/-0.9 years), performed a maximal 400 m swimming test and a simulated synchronized swimming routine. Oxygen uptake (VO(2)) of the tests was obtained by backward extrapolation of a monoexponential curve fitted to the postexercise oxygen uptake data.

RESULTS

There were no differences in VO(2) at the end of the routine (37.4+/-2.7 vs 40.5+/-2 mL . kg(-1) . min(-1), or 81.8+/-3.1% and 85.8+/-2.7% of VO(2peak)) and blood lactate (5.7+/-0.9 vs 4.5+/-0.4 mmol.L(-1)) between senior and comen synchronized swimmers. There was no difference in the half-time of V.O(2) decay (T(1/2)) between the athletes of the two categories, but T(1/2) was significantly higher after the routine compared with the V.O(2peak) test for both categories (senior: 45.2+/-5.9 vs 33.1+/-2.1 s, P<0.05, comen: 38.2+/-6 vs 27.4+/-8.2 s, P<0.05). The mean end-tidal pressure of CO(2) during the second half of the recovery was higher after the routine than after the VO(2peak) test (37.2+/-1.4 vs 34.5+/-1.5 mmHg, P<0.05), possibly due to the prolonged periods of breath holding (55+/-4% of routine time). Breathing frequency was also high (30+/-2.2 breaths . min(-1)) at the later part of recovery after the routine.

CONCLUSION

Cardiorespiratory and metabolic responses to a simulated synchronized swimming routine were similar in senior and comen athletes. The slower recovery of V.O(2)after the routine could be related to the elevated cost of ventilation, especially during the later stages of recovery, possibly as a result of the prolonged apnea.

Influence of resistive load on power output and fatigue during intermittent sprint cycling exercise in children

This study examined the effects of two resistive loads on fatigue during repeated sprints in children. Twelve 11.8 (0.2) year old boys performed a force-velocity test to determine the load (Fopt) corresponding to the optimal pedal rate. On two separate occasions, ten 6-s sprints interspersed with 24-s recovery intervals were performed on a friction-loaded cycle ergometer, against a load equal to Fopt or 50%Fopt. Although mean power output (MPO) was higher in the Fopt [397 (24) and 356 (19) W, P < 0.01], the decline in MPO over the 10 sprints was similar in Fopt [8.8 (1.9) %] and 50%Fopt [9.0 (2.4) %]. In contrast, peak power (PPO) was not different in sprint 1 between the two conditions [459 (24) and 460 (28) W], but was decreased only in 50%Fopt [11.4 (3.2) %, P < 0.01], while it was maintained in the Fopt despite the higher total work during each sprint. Fatigue within each sprint (percent drop from peak to end power output) was also higher in the 50%Fopt compared with the Fopt [32 (2.5) vs. 10 (1.6) %, P < 0.01]. Peak and mean pedal rate in Fopt condition were close to the optimum (Vopt), while a large part of the sprint time in 50%Fopt was spent far from Vopt. The present study shows that sprinting against Fopt reduces fatigue within and between repeated short sprints in children. It is suggested that fatigue during repeated sprints is modified when pedal rate is not close to Vopt, according to the parabolic power versus pedal rate relationship.

Type I insulin-like growth factor receptor signaling in skeletal muscle regeneration and hypertrophy

Skeletal muscle is able not only to increase its mass as an adaptation to mechanical loading generated by and imposed upon muscle but also to regenerate after damage, via its intrinsic regulation of gene transcription. Both cellular processes, muscle regeneration and hypertrophy, are mediated by the activation, proliferation and differentiation of muscle satellite cells and appear to be modulated by the mitotic and myogenic activity of locally produced insulin-like growth factor 1 (IGF-1), which functions in an autocrine/paracrine mode. Differentiation of satellite cells into myoblasts involves the regulation of skeletal muscle-specific proteins belonging to the family of myogenic regulatory factors (MRFs). The endocrine, autocrine and paracrine functions of IGF-1 are mediated through binding to the type I IGF receptor (IGF-1.R), which is a ligand-activated receptor tyrosine kinase. The binding of IGF-1 to IGF-1.R induces its autophosphorylation, which recruits specific cytoplasmic molecules containing the Insulin Receptor Substrate Proteins (IRS). The recruitment of IRS proteins by IGF-1/IGF-1.R binding is a critical level at which the proliferative and differentiative actions of IGF-1 diverge. Specific signaling pathways downstream of IGF-1, potentially involved in the mitogenic and myogenic responses and mediating skeletal muscle protein synthesis and hypertrophy following exercise-induced muscle overloading and damage, are discussed. A potential alternative activation of different signaling pathway(s) via a different receptor remains to be demonstrated.

Effects of two different short-term training programs on the physical and technical abilities of adolescent basketball players

This study evaluated and compared the effectiveness of two different off-season, short-term basketball training programs on physical and technical abilities of young basketball players. Twenty-seven adolescent basketball players (14.7+/-0.5 years; Tanner stage: 3.5+/-0.5) were randomly divided into a specialized basketball training group (SP, n=10), a mixed basketball plus conditioning training group (MX, n=10) and a control group (n=7). Training included five sessions per week (100-120 min each) and was performed for 4 weeks. Maximal oxygen uptake was similarly improved after SP (4.9+/-1.8%) and MX (4.9+/-1.4%), but there was no effect on ventilatory threshold. Peak and mean power output measured during the Wingate test were also improved by a similar magnitude after SP (21+/-5%) and MX (15+/-6%). Trunk muscle endurance was equally increased (SP: 23+/-4%, MX: 25+/-5%), but arms endurance was improved significantly more after MX (50+/-11%) compared to SP (11+/-14%, p<0.05). Performance in four basketball technical skills was similarly increased (by 17-27%) in both groups, with a tendency for greater improvement of the SP groups in the technical skills of shooting and passing. These results indicate that a SP basketball training program, performed exclusively on-court was as effective as a MX training program in terms of aerobic and anaerobic fitness improvement. Furthermore, the decrease of the total on-court training time in the MX group resulted in a tendency for a smaller improvement of basketball technical skills. In conclusion, both SP and MX training are equally effective in order to limit and/or reverse the detraining effects that occur during the off-season in basketball.

The role of the insulin-like growth factor 1 (IGF-1) in skeletal muscle physiology

The human insulin-like growth factor-1 (IGF-1) gene gives rise to multiple, heterogeneous mRNA transcripts through a combination of multiple transcription initiation sites, alternative splicing and different polyadenylation signals. These IGF-1 mRNA transcripts code different isoforms of the precursor peptide of IGF-1 (IGF-1Ea, IGF-1Eb and IGF-1Ec or MGF in human skeletal muscle), which also undergo post-translational modification. There is increasing interest in differential expression and implication of IGF-1 isoforms in the regulation of muscle fiber regeneration and hypertrophy following mechanical overloading and damage. The identification of a locally expressed, loading- or damage-sensitive IGF-1 isoform in skeletal muscle was one of the most attractive developments in the context of the autocrine/paracrine actions of IGF-1. The concept that the competing processes of cellular proliferation and differentiation and the increased protein synthesis required for muscle repair or hypertrophic adaptation are regulated by a differential expression and by distinct roles of IGF-1 isoforms is discussed in the present review.

Heritability of neuromuscular performance and anaerobic power in preadolescent and adolescent girls

AIM

This study examined the effect of the level of maturation on the heritability indices for various neuromuscular, anaerobic and anthropometric parameters in females.

METHODS

Sixty healthy female twins, 30 preadolescent (PA) aged 12.3+/-0.3 years and 30 adolescent (A) aged 16.7+/-0.2 years, with similar environmental backgrounds took part in the study. The magnitude of the genetic component was studied using a heritability index (HI) determined by the twin model. Chronological and skeletal age, biological maturation and age at menarche were used as criteria for the formation of the 2 groups. Zygosity was determined on the basis of morphological and dermatoglyphic similarity and by the identity in red blood cell antigens.

RESULTS

Almost all variables differed between PA and A group (P<0.05-0.01), with the exception of peak and mean power output expressed per unit fat free mass and fatigue index during the Wingate test. Most anthropometric characteristics had a high HI (0.8-0.99) in both groups. However, HI for peak blood lactate was higher in the A compared with the PA twins (0.98 vs 0.73). Furthermore HI for peak isokinetic torque at all angular velocities tested was also higher and significant (0.54 to 0.9) only for the A compared to the PA group.

CONCLUSIONS

The level of maturation affected the HI of some but not all neuromuscular and anaerobic performance variables. The higher HI for peak blood lactate and isokinetic torque in A compared with PA females may be explained by differences in the maturation of anaerobic metabolism and neuromuscular activation. Most HI for neuromuscular, anaerobic and anthropometric parameters were high, implying a strong genetic influence in these variables.

Recovery of power output and heart rate kinetics during repeated bouts of rowing exercise with different rest intervals

This study examined the effect of recovery time on the maintenance of power output and the heart rate response during repeated maximal rowing exercise. Nine male, junior rowers (age: 16 ± 1 years; body mass: 74.0 ± 9.1 kg; height: 1.78 ± 0.03 m) performed two consecutive all-out 1000 m bouts on a rowing ergometer on three separate occasions. The rest interval between the two bouts was 1.5 (INT1.5), 3 (INT3) and 6 min (INT6), allocated in random order. Power output was averaged for each 1000 m bout and for the first and last 500 m of each bout. Heart rate kinetics were determined using a two-component exponential model. Performance time and mean power output for the first bout was 209 ± 3 s and 313 ± 10 W respectively. Recovery of mean power output was incomplete even after 6 min (78 ± 2, 81 ± 2 and 84 ± 2 % for INT1.5, INT3 and INT6 respectively). Mean power output after INT6 was higher (p < 0.01) only compared with INT1.5. Power output during the first 500 m of bout 2 after INT6 was 10% higher compared with the second 500 m. During INT1.5 and INT3 power output during the first and the second 500 m of bout 2 was similar. Peak heart rate (~197 b·min(-1)) and the HR time constant (~13 s) were unaffected by prior exercise and recovery time. However, when the recovery was short (INT1.5), HR during the first 50 s of bout 2 was significantly higher compared with corresponding values during bout 1. The present study has shown that in order to maintain similar power outputs during repeated maximal rowing exercise, the recovery interval must be greater than 6 min. The influence of a longer recovery time (INT6) on maintenance of power output was only evident during the first half of the second 1000 m bout. Key PointsThe recovery of mean power output during two repeated maximal 1000 m bouts of rowing exercise was incomplete even after a 6 min rest interval.The benefit of the longer rest interval was apparent only during the first 500 m of bout 2.The HR time constant was unaffected by prior exercise and the time of recovery. However, when the recovery was short, HR during the first 50 s of bout 2 was significantly higher compared with the corresponding values of bout 1.

Changes in the angle-force curve of human elbow flexors following eccentric and isometric exercise

The aim of this study was to explore and compare the magnitude and time-course of the shift in the angle-force curves obtained from maximal voluntary contractions of the elbow flexors, both before and 4 consecutive days after eccentric and isometric exercise. The maximal isometric force of the elbow flexors of fourteen young male volunteers was measured at five different elbow angles between 50 degrees and 160 degrees . Subjects were then divided into two groups: the eccentric group (ECC, n=7) and the isometric group (ISO, n=7). Subjects in the ECC group performed 50 maximal voluntary eccentric contractions of the elbow flexors on an isokinetic dynamometer (30 degrees x s(-1)), while subjects in the ISO group performed 50 maximal voluntary isometric muscle contractions with the elbow flexors at a lengthened position. Following the ECC and ISO exercise protocols, maximal isometric force at the five angles, muscle soreness, and the relaxed (RANG) and flexed (FANG) elbow angles were measured at 24 h intervals for 4 days. All results were presented as the mean and standard error, and a quadratic curve was used to model the maximal isometric force data obtained at the five elbow angles. This approach not only allowed us to mathematically describe the angle-force curves and estimate the peak force and optimum angle for peak force generation, but also enabled us to statistically compare the shift of the angle-force curves between and within groups. A large and persistent shift of the angle-force curve towards longer muscle lengths was observed 1 day after eccentric exercise ( P<0.01). This resulted in a approximately 16 degrees shift of the optimum angle for force generation, which remained unchanged for the whole observation period. A smaller but also persistent shift of the angle-force curve was seen after isometric exercise at long muscle length ( P<0.05; shift in optimum angle approximately 5 degrees ). ECC exercise caused more muscle damage than ISO exercise, as indicated by the greater changes in RANG and ratings of muscle soreness ( P<0.05). It was suggested that the shift in the angle-force curve was proportional to the degree of muscle damage and may be explained by the presence of overstretched sarcomeres that increased in series compliance of the muscle.

Angle-specific impairment of elbow flexors strength after isometric exercise at long muscle length

In this study, we examined the long-term reductions in maximal isometric force (MIF) caused by a protocol of repeated maximal isometric contractions at long muscle length. Furthermore, we wished to ascertain whether the reductions in MIF are dependent on muscle length--that is, are the reductions in MIF more pronounced when the muscle contracts at a short length. The MIF of the elbow flexors of seven young male volunteers was measured at five different elbow angles between 50 degrees and 160 degrees. On a separate day, the participants performed 50 maximal voluntary isometric muscle contractions with the elbow flexors at a lengthened position; that is, with the shoulder hyperextended at 45 degrees and the elbow joint fixed at 140 degrees. Following this exercise, the MIF at the five elbow angles, range of motion, muscle soreness and plasma creatine kinase activity were measured at 24 h intervals for 4 days. On day 1, the decline in MIF was higher at the more acute elbow angles of 50 degrees (42 +/- 8%) and 70 degrees (39 +/- 8%; both P<0.01) than at 90 degrees (26 +/- 4%) and 140 degrees (16 +/- 3%; both P<0.01). No significant reduction in MIF was evident at an elbow angle of 160 degrees. Maximal isometric force at an elbow angle of 140 degrees was fully restored on day 3, whereas at an angle of 50 degrees it remained depressed for the 4 day observation period. Restoration of MIF was a function of the elbow angle, with force recovery being less at the smaller angles. The range of motion was decreased by 14 +/- 2 degrees on day 1 (P<0.01) and did not return to baseline values by day 4. Muscle soreness ratings remained significantly elevated for the 4 day period. Serum creatine kinase peaked on day 1 (522 +/- 129 IU, P<0.01) and decreased thereafter. We conclude that the disproportionate decrease in MIF at the small elbow angles and the length-specific recovery in MIF after repeated maximal isometric contractions at long muscle length may be explained by the presence of overstretched sarcomeres that increased in series compliance of the muscle, therefore causing a rightward shift of the force-length relationship.