P V Komi’s research while affiliated with University of Jyväskylä and other places

The Achilles tendon moment arm (MA_AT) and foot lever ratio (FLR) can play important roles for force production and movement economy during locomotion. This notion has become more relevant, and suggestion has been given that the Kenyan runners belonging to the world elite would have specific anatomical, mechanical, and functional properties in their lower limbs and that this feature could be responsible for their high running economy. The present study aimed to characterize the AT of elite Kenyan distance runners as compared with Japanese ones, and to examine the potential relationship with their running performance. Ultrasonography was used to measure AT cross-sectional area and AT soleus and gastrocnemius lengths. MA_AT and FLR were calculated from the position of anatomical landmarks using sagittal plane photographs. MA_AT was significantly longer and the FLR lower in Kenyans than in Japanese. Independently of the group, the running performance was positively related to the MA_AT (r = 0.55, P < 0.001) and negatively to the FLR (r = −0.45, P = 0.002). These results suggest that longer MA_AT and lower FLR could be advantageous in elite Kenyan runners, by contributing to effective endurance running performance in a protective and economical way.

The present study examined the muscle-tendon interaction of ten international level Kenyan runners. Ultrasonography and kinematics were applied together with EMG recordings of lower limb muscles during repetitive hopping performed at maximal level. The ten Kenyans had longer gastro Achilles tendon at rest (p < 0.01) as compared with ten control subjects matched in height. Conversely, the stretching and shortening amplitudes of the tendinous tissues of the medial gastrocnemius (MG) muscle were significantly smaller in the Kenyans than in controls during the contact phase of hopping. This applied also to the fascicle length changes, which were smaller and more homogeneous among Kenyans. These limited musculo-tendinous changes resulted in higher maximal hopping height and in larger power despite their reduced body weight. The associated finding of a greater shortening to stretching ratio of the MG tendinous tissues during contact could imply that the Kenyan MG muscle-tendon unit is optimized to favor efficient storage and recoil of elastic energy, while operating at optimal muscle fascicle working range (plateau region).

Aging is related to multiple changes in muscle physiology and function. Previous findings concerning the effects of aging on motor unit discharge rate (DR) and fluctuations in DR and force are somewhat contradictory. Eight YOUNG and nine OLD physically active males performed isometric ramp (RECR) and isotonic (ISO) plantar flexions at 10 and 20% of surface EMG at MVC. Motor unit (MU) action potentials were recorded with intramuscular fine-wire electrodes and decomposed with custom build software "Daisy". DR was lower in OLD in RECR-10% (17.9%, p<0.001), RECR-20% (15.8%, p<0.05), ISO-10% (17.7%, p<0.01) and ISO-20% (14%, n.s.). In YOUNG force fluctuations were smaller at ISO-10% (72.1%, p<0.001) and ISO-20% (55.2%, p<0.05) which were accompanied with a slight increase in DR variation (n.s.). The observed lower DR in OLD is in line with earlier findings in small distal muscles. Also the larger force fluctuation in OLD was in line with previous studies with smaller hand muscles. These findings suggest that the age-related changes in MU control do exist also in large leg extensors that play an important role in human locomotion and balance control.

The present study investigated the regulation of leg and joint stiffness in hopping at different intensity levels. Eight male subjects performed bilateral hopping at various intensity levels that were determined by peak vertical ground reaction force (GRF). In addition to the GRF, the measurements included hopping kinematics and electromyography (EMG) of selected leg muscles. While the leg and ankle joint stiffness remained invariant, the knee joint stiffness increased significantly (P<0.01) with the hopping intensity. EMG analysis revealed a significant increase in averaged EMG for all the measured muscles before and during the early phase of ground contact (P<0.05-0.001) with increasing hopping intensity. However, only the vastus lateralis muscle showed significant increase in stretch reflex EMG with increasing hopping intensity (P<0.01). The present study indicates that in hopping with short contact time the leg stiffness modulation is sensitive to changes in ankle joint stiffness and the role of knee joint stiffness is to regulate the jumping performance (height). Furthermore, our results suggest that leg and joint stiffness in hopping is mainly adjusted by centrally programmed motor commands and the contribution of stretch reflexes to muscle force output is muscle-dependent.

In animal studies, bone adaptation has been initiated successfully without the transient force spike associated with high impact exercises. Consequently, a 12-week bilateral hopping on the balls of the feet intervention was conducted. 25 elderly men (age 72(SD4) years, height 171(6) cm, weight 75(9) kg) were randomly assigned into exercise and control groups. Ten subjects in each group completed the study. Carboxyterminal propeptide of type I collagen (CICP), bone-specific alkaline phosphatase (bALP) and carboxyterminal telopeptide of type I collagen (CTx) were measured from venous blood samples at baseline, at 2 weeks and at the end of the intervention. Maximal ground reaction force (GRF), osteogenic index (OI) and jump height (JH) were determined from bilateral hopping test and balance was assessed with velocity of center of pressure (COP(velocity)) while standing on the preferred leg with eyes open. The intervention consisted of 5-7 sets of 10 s timed bilateral hopping exercise at 75-90% intensity three times/week. There was no significant group × time interaction for GRF, OI and JH (P = 0.065). GRF (11% change from baseline vs. 4%), OI (15 vs. 6%) and COP(velocity) (-10 vs. -1%) were not influenced by the intervention (P > 0.170), while the control group improved JH (P = 0.031) (2 vs. 18%). For the biomarkers, no effect was observed in MANOVA (P = 0.536) or in univariate analyses (P = 0.082 to P = 0.820) (CICP -2 vs. -3%, CTx 8 vs. -12%, bALP 0 vs. -3.7%). Allowing transient impact force spikes may be necessary to initiate a bone response in elderly men as the intervention was ineffective.

It was hypothesized that exercise-induced muscle damage (EIMD)-related alterations in hormonal responses could be observed if a second exercise bout is performed soon after an identical unaccustomed bout leading to delayed onset muscle soreness (DOMS). Eight men (31 ± 7 years) and eight boys (14 ± 0 years) performed two exercise bouts (E1 and E2, with 48 h rest in between) consisting of three sets of bilateral knee extensions until exhaustion with 40% load. No differences between the groups or bouts were observed in the number of repetitions performed and maximal isometric force decline, or between groups in serum creatine kinase activity and DOMS. Decreased peak epinephrine (EPI) (-38%), growth hormone (GH) (-45%) and cortisol (COR) (-31%) concentrations were found in E2 in men (P<0.05). In men, the peak GH concentration was also lower in E2 and COR was higher in both bouts than in boys. No changes in norepinephrine and testosterone responses were found in either group. The results suggest that in men, the responses of EPI, GH and COR are attenuated when the second bout is performed under the influence of DOMS. In boys, the lack of this attenuation may not be explained by less severe EIMD.

Both contraction type and ageing may cause changes in H-reflex excitability. H reflex is partly affected by presynaptic inhibition that may also be an important factor in the control of MU activation. The purpose of the study was to examine age related changes in H-reflex excitability and motor unit activation patterns in dynamic and in isometric contractions. Ten younger (YOUNG) and 13 elderly (OLD) males performed isometric (ISO), concentric (CON) and eccentric (ECC) plantarflexions with submaximal activation levels (20% and 40% of maximal soleus surface EMG). Intramuscular EMG data was analyzed utilizing an intramuscular spike amplitude frequency histogram method. Average H/M ratio was always lowest in ECC (n.s.). Mean spike amplitude increased with activation level (P<.05), whereas no significant differences were found between contraction types. Both H-reflex excitability, which may be due to an increase in presynaptic inhibition, and mean spike frequency were higher in YOUNG compared to OLD. In OLD the mean spike frequency was significantly smaller in CON compared to ISO. Lack of difference in mean spike amplitude and frequency across contraction types in YOUNG would imply a similar activation strategy, whereas the lower frequency in dynamic contractions in OLD could be related to synergist muscle behavior.

The osteogenicity of a given exercise may be estimated by calculating an osteogenic index (OI) consisting of magnitude and rate of strain. Volleyball involves repetitive jumping and requires high power output and thus may be expected to be beneficial to bone and performance. The purpose of the present study was to examine if habitual volleyball playing is reflected in OI. Ten elderly habitual volleyball players [age 69.9 (SD 4.4) years] and ten matched controls volunteered [age 69.7 (4.2) years] as subjects. Distal tibia (d), tibial mid-shaft (50) and femoral neck (FN) bone characteristics were measured using pQCT and DXA. To estimate skeletal rigidity, cross-sectional area (ToA(50)), and compressive (BSI(d)) and bending strength indices (SSImax(50)) were calculated. Maximal performance was assessed with eccentric ankle plantar flexion, isometric leg press and countermovement jump (CMJ). A fast Fourier transform (FFT) was calculated from the acceleration of the center of mass during the CMJ. Maximal acceleration (MAG) and mean magnitude frequency (MMF) were selected to represent the constituents of OI. OI was calculated as the sum of the products of magnitudes and corresponding frequencies. Volleyball players had 7% larger ToA(50) and 37% higher power in CMJ, 15% higher MAG and 36% higher OI (P <or= 0.047) than the matched controls. No difference was observed in leg press, plantar flexion or the MMF (P >or= 0.646). In conclusion, habitual volleyball players may be differentiated from their matched peers by their dynamic jumping performance, and the differences are reflected in the magnitude but not rate of loading.