Signalling control strength

Metabolic control analysis (MCA) has become what it is, largely because the special organization of living cells led to rather specific questions. These questions focused on the role of enzymes, genes, and, in subsequent generalizations, on well-defined process activities. With an emphasis on the work by Heinrich and co-workers, the theory behind MCA is summarized in a way that leads naturally to its extensions to hierarchical systems, such as gene expression and signal transduction, and to control beyond the steady state. The analysis of the control properties of signal transduction cascades is reviewed with an emphasis on the relative importance of the protein kinases and the protein phosphatases. The two types of enzyme are both important for the amplitude of signal transduction, whereas phosphatases may be more important for the later phases of signal transduction and for its duration. Novel MCA of concentrations and fluxes that vary with time is explicated. It is concluded that the clarity and operationality of concepts such as control strength (now control coefficient) plus the clear theoretical frameworks provided by Heinrich and colleagues, should enable us greatly to reduce the Babylonian confusion that could otherwise occur in the data deluges of Systems Biology.     

Manual abilities of the elderly--handgrip strength, finger and thumb push strength and opening strength in age comparison

The purpose of this paper is to display the static strength capacities of healthy adults in different age categories. A total of 279 healthy German adults at the ages of 20 to 29 years, 50 to 59 years and 60 to 69 years generated their maximum static handgrip, index finger and thumb push strength, as well as their maximum opening strength on a smooth jar lid of 85 mm diameter and on a knurled bottle lid of 31 mm with their right hand. The results show larger male strength than female strength. Significant age-induced differences appear primarily in opening strengths between the age groups 20 to 29 and 50 to 59 years in male subjects and in female opening strengths between the age groups 20 to 29 and 60 to 69 years as well as between the age groups 50 to 59 and 60 to 69 years. Of greatest interest is that elderly men show the largest opening strengths.     

Isokinetic strength in weight-trainers

Isokinetic strength of ankle plantarflexion (APF), knee extension (KE) and elbow extension (EE) was measured in male weight-trainers (6 power-lifters and 7 bodybuilders) and 25 untrained men of similar age and height. The weight-trainers exceeded control subjects by 21%, 25% and 73% in APF, KE and EE strength respectively. A similar pattern was obtained for limb girth, in which the weight-trainers exceeded control subjects by 6%, 13%, and 31% in calf, thigh and arm girth, respectively. Strength was similarly enhanced in the weight-trainers at the lower and higher velocities (APF 0.10, 0.63 rad X s-1, KE and EE 0.52, 3.14 rad X s-1) tested, and accounted for the positive correlation (r = 0.84) observed between low and high velocity strength. The powerlifters differed significantly from the bodybuilders only in their greater low velocity APF strength. The relatively greater enhancement of upper versus lower limb strength and muscle mass in the weight-trainers was considered in respect to training habits, trainability of different muscle groups and the state of training of muscle groups in untrained men.     

Acute effect of two aerobic exercise modes on maximum strength and strength endurance

The purpose of this study was to evaluate the effects of 2 modes of aerobic exercise (continuous or intermittent) on maximum strength (1 repetition maximum, 1RM) and strength endurance (maximum repetitions at 80% of 1RM) for lower- and upper-body exercises to test the acute hypothesis in concurrent training (CT) interference. Eight physically active men (age: 26.9 +/- 4.2 years; body mass: 82.1 +/- 7.5 kg; height: 178.9 +/- 6.0 cm) were submitted to: (a) a graded exercise test to determine V(.-)O2max (39.26 +/- 6.95 ml x kg(-1) x min(-1)) and anaerobic threshold velocity (3.5 mmol x L(-1)) (9.3 +/- 1.27 km x h(-1)); (b) strength tests in a rested state (control); and (c) 4 experimental sessions, at least 7 days apart. The experimental sessions consisted of a 5-kilometer run on a treadmill continuously (90% of the anaerobic threshold velocity) or intermittently (1:1 minute at V(.-)O2max). Ten minutes after the aerobic exercise, either a maximum strength or a strength endurance test was performed (leg press and bench press exercises). The order of aerobic and strength exercises followed a William's square distribution to avoid carryover effects. Results showed that only the intermittent aerobic exercise produced an acute interference effect on leg strength endurance, decreasing significantly (p < 0.05) the number of repetitions from 10.8 +/- 2.5 to 8.1 +/- 2.2. Maximum strength was not affected by the aerobic exercise mode. In conclusion, the acute interference hypothesis in concurrent training seems to occur when both aerobic and strength exercises produce significant peripheral fatigue in the same muscle group.     

Serum hormones in male strength athletes during intensive short term strength training.

Training-induced adaptations in the endocrine system and strength development were investigated in nine male strength athletes during two separate 3-week intensive strength training periods. The overall amount of training in the periods was maintained at the same level. In both cases the training in the first 2 weeks was very intensive: this was followed by a 3rd week when the overall amount of training was greatly decreased. The two training periods differed only in that training period I included one daily session, while during the first 2 weeks of period II the same amount of training was divided between two daily sessions. In general, only slight and statistically insignificant changes occurred during training period I in mean concentrations of serum hormones examined or sex hormone-binding globulin as well as in maximal isometric leg extensor force. However, during training period II after 2 weeks of intensive strength training a significant decrease (P less than 0.05) was observed in serum free testosterone concentration [from 98.4 (SD 24.5) to 83.8 (SD 14.7) pmol.l-1] during the subsequent week of reduced training. No change in the concentration of total testosterone was observed. This training phase was also accompanied by significant increases (P less than 0.05) in serum luteinizing hormone (LH) and cortisol concentrations. After 2 successive days of rest serum free testosterone and LH returned to (P less than 0.05) their basal concentrations. Training period II led also to a significant increase (P less than 0.05) [from 3942 (SD 767) to 4151 (SD 926) N] in maximal force.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of time-of-day-specific strength training on serum hormone concentrations and isometric strength in men

A time-of-day influence on the neuromuscular response to strength training has been previously reported. However, no scientific study has examined the influence of the time of day when strength training is performed on hormonal adaptations. Therefore, the primary purpose of this study was to examine the effects of time-of-day-specific strength training on resting serum concentrations and diurnal patterns of testosterone (T) and cortisol (CORT) as well as maximum isometric strength of knee extensors. Thirty eight diurnally active healthy, previously untrained men (age 20-45 yrs) underwent a ten-week preparatory strength training period when sessions were conducted between 17:00-19:00 h. Thereafter, these subjects were randomized into either a morning (n=20, training times 07:00-09:00 h) or afternoon (n=18, 7:00-19:00 h) training group for another ten-week period of time-of-day-specific training (TST). Isometric unilateral knee extension peak torque (MVC) was measured at 07:00, 12:00, 17:00, and 20:30 h over two consecutive days (Day 1 & Day 2) before and after TST. Blood samples were obtained before each clock-time measurement to assess resting serum T and CORT concentrations. A matched control group (n=11) did not train but participated in the tests. Serum T and CORT concentrations significantly declined from 07:00 to 20:30 h on all test days (Time effect, p<.001). Serum CORT at 07:00 h was significantly higher on Day 1 than Day 2 in the control and afternoon group, both in Pre and Post conditions (Day x Time interaction, p<.01). In the morning group, a similar day-to-day difference was present in the Pre but not Post conditions (Time x Group interaction, p<.05). MVC significantly increased after TST in both the morning and afternoon groups (Pre to Post effect, p<.001). In both groups, a typical diurnal variation in MVC (Time effect, p<.001) was found, especially on Day 2 in the Pre condition, and this feature persisted from Pre to Post in the afternoon group. In the morning group, however, diurnal variation was reduced after TST on both Day 1 and Day 2 (Pre to PostxDay x TimexGroup interaction, p<.05). In conclusion, 10 weeks of morning time-of-day-specific strength training resulted in reduced morning resting CORT concentrations, presumably as a result of decreased masking effects of anticipatory psychological stress prior to the morning testing. The typical diurnal pattern of maximum isometric strength was blunted by the TST period in the morning but not the afternoon group. However, the TST period had no significant effect on the resting total T concentration and its diurnal pattern and on the absolute increase in maximum strength.     

Bone strength in hypokinesia]

Experiments (20- and 100-day) on rats showed that decrease of the animal motor activity with preserved static function of the extremities led to a marked thinning of the cortical layer of the femoral bone. However, the ability of the whole bone to bear mechanical load decreased but slightly. An increase in the firmness of the bone tissue as a result of its mineralization compensated for the cortical layer thinning.     

Molecular determinants of sink strength

The manipulation of sink to source relations has been subject to extensive plant breeding programs aiming to improve harvest index and thereby crop yield. The introduction of molecular and biochemical tools has enabled scientists to investigate the underlying principles. This has opened up the fascinating possibility of identifying molecular determinants of sink strength and to further increase yield on a rational basis. In the past, transgenic plants with alterations in the activity of only one putative molecular determinant have been created and this strategy has not resulted in substantial and reliable increases in yield. Yet, careful molecular and biochemical investigations have provided valuable insight about carbon flux into different metabolic pathways at different stages of sink development and it has become apparent that this metabolic channelling needs to be exploited by using stage- and cell-specific promoters in attempts to increase sink strength.     

Physical strength predicts political violence

Research has revealed an association between individual physical strength and attitudinal support for modern war. Physical strength of one individual has an infinitesimal effect on the outcomes of state-level aggression involving large-scale armies and complex military technology. The fact that stronger individuals do support such aggression hints at an evolved psychology specialized for small-scale coalitional aggression, where strength of coalition members non-negligibly contribute to the net coalition strength. Here, I examined whether strength also accounts for participation in modern political aggression, as contrasted to mere support. Given that contemporary political aggression primarily occurs within—not between—states, I focused on intra-state forms of political violence, specifically violent antigovernment protests. To enhance external and ecological validity, I relied on large probability samples from both non-WEIRD and WEIRD countries experiencing political violence (N = 6283; interviewees were quota-sampled from YouGov online panels to generate representative samples of online adult populations). Multinational analyses revealed that self-perceived strength significantly predicts intentions to participate in political violence and self-reported participation, and that this association is stronger among young interviewees, but not among men (compared to women). The predictive power of strength was modest but comparable to that of gender, an established predictor of aggression. I discuss why the fact that strength—a physiological variable—relates to political violence—a complex modern phenomenon—is remarkable. Subsequently, I suggest a new research agenda that draws on insights from evolutionary research to study modern political violence.     

The influence of strength, flexibility, and simultaneous training on flexibility and strength gains

The purpose of this study was to examine the strength and flexibility gains after isolated or simultaneous strength and flexibility training after 16 weeks. Eighty sedentary women were randomly assigned to 1 of 4 groups: strength training (ST; n = 20), flexibility training (FLEX) (n = 20), combination of both (ST + FLEX; n = 20) and control group (CG; n = 20). All the groups performed pre and posttraining sit and reach test to verify the flexibility level and 10RM test for leg press and bench press exercises. The training protocol for all groups, except for the CG, included 3 weekly sessions, in alternated days, totaling 48 sessions. Strength training was composed of 8 exercises for upper and lower body, executed in 3 sets of periodized training. The flexibility training was composed of static stretching exercises that involved upper and lower body. Results showed that ST (30 ± 2.0 to 36 ± 3.0 cm), ST + FLEX (31 ± 1.0 to 42 ± 4.0 cm), and FLEX (32 ± 3.0 to 43 ± 2.0 cm) significantly increased in flexibility in relation to baseline and to CG (30 ± 2.0 to 30 ± 2.0 cm); however, no significant differences were observed between the treatment conditions. Strength tests demonstrated that ST and ST + FLEX significantly increased 10RM when compared to baseline, FLEX, and the CG. In conclusion, short-term strength training increases flexibility and strength in sedentary adult women. Strength training may contribute to the development and maintenance of flexibility even without the inclusion of additional stretching, but strength and flexibility can be prescribed together to get optimal improvements in flexibility.     

Neural training for quick strength gains in the elderly: strength as a learned skill

A sample of 20 older adults (76 +/- 6 years) participated in a two-session training intervention with the goal of eliciting rapid and functionally meaningful strength gains in the ankle plantarflexors. Tests were conducted on a Monday-Wednesday-Friday schedule with two training sessions after tests one and two. During each test, subjects performed five maximal explosive force production contractions (MVCs) from which maximal voluntary torque (MVT) and peak rates of torque development (RTDs) were obtained. To augment the quick strength gains typically observed in response to serial strength measurements, these MVCs were supplemented with exercises consisting of high-velocity, low-force movements at the ankle joint. These exercises were chosen to elicit high rates of neural stimulation without high resistance. Maximal voluntary torque increased by 15% from 53.9 +/- 36 to 62.2 +/- 36.2 N x m (p = 0.02). There was a parallel trend toward increases in RTD based on RTD measures computed over various timescales (0.11 < p < 0.21). The nonsignificant increase in RTD was from 223.9 +/- 153.6 to 248.4 +/- 147.8 N x m x s(-1). This preliminary study has determined that rapid strength gains of functional magnitude are possible in the plantarflexors of the elderly. Subsequent work is necessary to test the translation of such gains to function in the frail elderly and to determine the specific contributions of the selected low-resistance exercises to overall gains.