Ole Kristian Brones Berg

• Tøien, Tiril; Lindberg Nielsen, Jakob; Berg, Ole Kristian Brones; Brobakken, Mathias Forsberg; Nyberg, Stian Kwak & Espedal, Lars [Vis alle 10 forfattere av denne artikkelen] (2023). The impact of life-long strength versus endurance training on muscle fiber morphology and phenotype composition in older men. Journal of applied physiology. ISSN 8750-7587. 135(6), s. 1360–1371. doi: 10.1152/japplphysiol.00208.2023.
• Laginestra, Fabio Giuseppe; Berg, Ole Kristian; Nyberg, Stian Kwak; Venturelli, Massimo; Wang, Eivind & Helgerud, Jan (2023). Stroke volume response during prolonged exercise depends on left ventricular filling : evidence from a beta-blockade study. American Journal of Physiology. Regulatory Integrative and Comparative Physiology. ISSN 0363-6119. 325(2), s. R154–R163. doi: 10.1152/ajpregu.00293.2022. Vis sammendrag

  Prolonged moderate intensity exercise leads to a progressive upward drift in heart rate (HR) that may compromise stroke volume (SV). Alternatively, the HR drift may be related to abated SV due to impaired ventricular function. The aim of this study was to examine the effects of cardiovascular drift on left ventricular volumes and in turn SV. Thirteen healthy young males completed two 60-minute cycling bouts on a semi-recumbent cycle ergometer at 57%VO2max either under placebo condition (CON) or after ingesting a small dose of β1-blockers (BB). Measurements of HR, end-diastolic volume (EDV), and end-systolic volume were obtained by echocardiography and used to calculate SV. Other variables such as ear temperature, skin temperature, blood pressure, and blood volume were measured to assess potential changes in thermoregulatory needs and loading conditions. HR drift was successfully prevented when using BB from min10 to min60 (128±9 to 126±8bpm, p=0.29) but not in CON (134±10 to 148±10bpm, p<0.01). Conversely, during the same time, SV increased by 13% when using BB (103±9 to 116±7mL, p<0.01) while it was unchanged in CON (99±7 to 101±9mL, p=0.37). The SV behavior was mediated by a 4% increase in EDV in the BB condition (164±18 to 170±18mL, p<0.01), while no change was observed in the CON condition (162±18 to 160±18mL, p=0.23). In conclusion, blocking HR drift enhances EDV and SV during prolonged exercise. These findings suggest that SV behavior is tightly related to filling time and loading conditions of the left ventricle.

• Pedrinolla, Anna; Berg, Ole Kristian; Tøien, Tiril & Wang, Eivind (2023). Aging increases metabolic capacity and reduces work efficiency during handgrip exercise in males. Journal of applied physiology. ISSN 8750-7587. 134(5), s. 1154–1164. doi: 10.1152/japplphysiol.00411.2022. Vis sammendrag

  Maximal oxygen uptake and exercise performance typically decline with age. However, there are indications of preserved vascular function and blood flow regulation during arm exercise. Yet, it is unknown if this potential physiological preservation with age is mirrored in peripheral metabolic capacity and V̇O2/watt ratio. Thus, to investigate the effects of aging in the arms, we measured metabolic and vascular responses to 6-minute bouts of dynamic handgrip exercise at 40% and 80% of maximal work rate (WRmax) in eleven young (26±2yr) and twelve old (80±6yr) males, applying Doppler-ultrasound combined with blood samples from a deep forearm vein. At baseline, old had a larger arterial diameter compared to young (p<0.001). During exercise, the two groups reached the same WRmax. V̇O2, blood flow, and oxygen supply were higher (40%WRmax; 80%WRmax, all p<0.01), and arterio-venous oxygen-difference lower (80%WRmax, p<0.02), in old compared to young. Old also had a higher oxygen-excess at 80%WRmax (p<0.01) than young, while no difference in muscle diffusion or oxygen-extraction was detected. Only young exhibited an increase in intensity-induced arterial dilation (p<0.05), and they had a lower mean arterial pressure than old at 80%WRmax (p<0.001). V̇O2/watt (40%WRmax; 80%WRmax) was reduced in old compared to young (both p<0.05). In conclusion, in old and young males with a similar handgrip WRmax, old had a higher V̇O2 during 80%WRmax intensity, achieved by an increased blood flow. This may be a result of the available cardiac output reserve, compensating for reduced work efficiency and attenuated vascular response observed in old.

• Tøien, Tiril; Unhjem, Runar Jakobsen; Berg, Ole Kristian; Aagaard, Per & Wang, Eivind (2022). Strength versus endurance trained master athletes : contrasting neurophysiological adaptations. Experimental Gerontology. ISSN 0531-5565. 171(January), s. 1–12. doi: 10.1016/j.exger.2022.112038. Vis sammendrag

  Neural factors play a critical role in the age-related decline in maximal strength and rate of force development (RFD). However, it is uncertain how the age-related attenuation in neuromuscular function may be mitigated in strength or endurance trained master athletes. In this study we applied evoked spinal motoneuron recordings to examine descending motor drive, i.e., efferent drive from supraspinal and spinal centres during maximal voluntary contraction (MVC; V-wave) and H-reflex excitability measured at 10 % MVC in older (>65 yrs) and younger (<35 yrs) strength athletes (n = 21), endurance athletes (n = 17) and untrained control participants (n = 30). Both strength (b = 0.09 [0.01–0.18], p = 0.038) and endurance training (b = 0.14 [0.04–0.23], p = 0.006) were associated with a high V-wave amplitude. This was likely explained by an elevated H-reflex excitability (b = 0.23 [0.11–0.35], p < 0.001) in endurance trained participants, which failed to be seen in strength trained participants. These contrasting neurophysiological properties were accompanied by different physiological traits; strength training was associated with high maximal strength (b = 107.5 [84.6 to 130.4] kg, p < 0.001) and RFD (b = 3171 [2248 to 4094] N‧s−1, p < 0.001), whereas endurance training was associated with elevated maximal oxygen uptake (V̇O2max; b = 13.6 [8.0–19.2] ml‧kg−1‧min−1, p < 0.001). This pattern was apparent irrespective of age, although all traits were negatively associated with advanced age (p < 0.05). In conclusion, strength trained individuals demonstrate higher descending motor drive (elevated V-wave responses), compared to age-matched untrained individuals. Endurance trained individuals also showed elevated V-wave responses, uniquely accompanied by enhanced α-motoneuron excitability and/or reduced pre/postsynaptic inhibition (elevated H-reflex responses). Since a high descending motor drive is a key component of strong muscle contractions, strength training should be emphasized to sustain the ability to carry out force-dependent tasks at older age. Keywords: lifelong strength training, descending motor drive, spinal motoneuron excitability, maximal muscle strength, rate of force development

• Haglo, Håvard Pedersen; Berg, Ole Kristian; Hoff, Jan; Helgerud, Jan & Wang, Eivind (2022). Maximal strength training in patients with inflammatory rheumatic disease: implications for physical function and quality of life. European Journal of Applied Physiology. ISSN 1439-6319. 122(7), s. 1671–1681. doi: 10.1007/s00421-022-04948-w. Fulltekst i vitenarkiv Vis sammendrag

  Purpose: Patients with inflammatory rheumatic disease (IRD) have attenuated muscle strength in the lower extremities, resulting in impaired physical function and quality of life. Although maximal strength training (MST), applying heavy resistance, is documented to be a potent countermeasure for such attenuation, it is uncertain if it is feasible in IRD given the pain, stiffness, and joint swelling that characterize the population. Methods: 23 patients with IRD (49 ± 13 years; 20 females/3 males), diagnosed with spondyloarthritis, rheumatoid arthritis, or systemic lupus erythematosus, were randomized to MST or a control group (CG). The MST group performed four × four repetitions dynamic leg press two times per week for 10 weeks at ~ 90% of one repetition maximum (1RM). Before and after training 1RM, rate of force development (RFD), and health-related quality of life (HRQoL) were measured. Results: Session attendance in the MST group was 95%, of which 95% conducted according to MST protocol. Furthermore, MST increased 1RM (29 ± 12%, p = 0.001) and early and late phase RFD (33–76%, p < 0.05). All improvements were different from the CG (p < 0.05). MST also resulted in HRQoL improvements in the dimensions; physical functioning, general health, and vitality (p < 0.05). Physical functioning was associated with 1RM (rho = 0.55, p < 0.01) and early phase RFD (rho = 0.53–0.71, p < 0.01; different from CG p < 0.05). Conclusions: Despite being characterized by pain, stiffness, and joint swelling, patients with IRD appear to tolerate MST well. Given the improvements in 1RM, RFD, and HRQoL MST should be considered as a treatment strategy to counteract attenuated muscle strength, physical function, and HRQoL.

• Haglo, Håvard Pedersen; Wang, Eivind; Berg, Ole Kristian; Hoff, Jan & Helgerud, Jan (2021). Smartphone-assisted high-intensity interval training in inflammatory rheumatic disease patients : randomized controlled trial. JMIR mhealth and uhealth. ISSN 2291-5222. 9(10), s. 1–16. doi: 10.2196/28124. Fulltekst i vitenarkiv Vis sammendrag

  Background: Patients with inflammatory rheumatic diseases (IRDs) experience disease-related barriers to physical training. Compared with the general population, IRD patients are reported to have reduced maximal oxygen uptake (VO2max) and physical activity levels. Supervised high-intensity interval training (HIIT) is documented to counteract the reduced VO2max and poor cardiovascular health associated with IRDs. However, supervised HIIT is resource demanding. Objective: This study sought to investigate if self-administered 4×4-min HIIT guided by a smartphone app (Myworkout GO) could yield similar HIIT-induced effects as standard 4×4-min HIIT performed under the guidance and supervision of health care professionals. The effects studied were on VO2max and health-related quality of life (HRQoL). Methods: Forty patients (33 female patients, mean age 48 years, SD 12 years; 7 male patients, mean age 52 years, SD 11 years) diagnosed with rheumatoid arthritis, spondyloarthritis, or systemic lupus erythematosus were randomized to a supervised group (SG) or an app group (AG). Both groups were instructed to perform 4×4-min intervals with a rate of perceived exertion of 16 to 17, corresponding to 85% to 95% of the maximal heart rate, twice a week for 10 weeks. Treadmill VO2max and HRQoL measured using RAND-36 were assessed before and after the exercise period. Results: VO2max increased (P<.001) in both groups after 10 weeks of HIIT, with improvements of 3.6 (SD 1.3) mL/kg/min in the SG and 3.7 (SD 1.5) mL/kg/min in the AG. This was accompanied by increases in oxygen pulse in both groups (P<.001), with no between-group differences apparent for either measure. Improvements in the HRQoL dimensions of bodily pain, vitality, and social functioning were observed for both groups (P<.001 to P=.04). Again, no between-group differences were detected. Conclusions: High-intensity 4×4-min interval training increased VO2max and HRQoL, contributing to patients’ reduced cardiovascular disease risk, improved health and performance, and enhanced quality of life. Similar improvements were observed following HIIT when IRD patients were guided using perceived exertion by health care professionals or the training was self-administered and guided by the app Myworkout GO. Utilization of the app may help reduce the cost of HIIT as a treatment strategy in this patient population.

• Berg, Ole Kristian; Stutzer, Jens-Meinhard; Hoff, Jan & Wang, Eivind (2021). Early maximal strength training improves leg strength and postural stability in elderly following hip fracture surgery. Geriatric Orthopaedic Surgery & Rehabilitation (GOS). ISSN 2151-4585. 12, s. 1–8. doi: 10.1177/21514593211015103. Fulltekst i vitenarkiv Vis sammendrag

  Introduction: Hip fractures predominantly occur in the geriatric population and results in increased physical inactivity and reduced independency, largely influenced by a downward spiral of ambulatory capacity, related to loss of skeletal muscle strength and postural stability. Thus, effective postoperative treatment, targeting improvements in muscle strength, is sought after. Materials & Methods: Twenty-one hip fracture patients (>65 yr) were randomized to 8 weeks of either conventional physiotherapy control group (CG), or leg press and hip abduction maximal strength training (MST) 3 times per week. MST was performed applying heavy loads (85-90% of 1 repetition maximum; 1RM) and 4-5 repetitions in 4 sets. Maximal strength (bi- and unilateral 1RM), postural stability (unipedal stance test; UPS), and DEXA-scan bone mineral content/ density (BMC/BMD) were measured before and after the 8-week rehabilitation. Results: Both MST and conventional physiotherapy improved bilateral leg press 1RM by 41 ± 27 kg and 29 ± 17 kg, respectively (both p < 0.01), while unilateral leg press 1RM only increased after MST (within group and between groups difference: both p < 0.05). MST also resulted in an increase in abduction 1RM in both the fractured (5 kg, 95%CI: 2-7; p < 0.01) and healthy limb (6 kg, 95%CI: 3-9; p < 0.01), while no such improvement was apparent in the CG (between groups difference: p < 0.01). Finally, MST improved UPS of the fractured limb (p < 0.05). No differences were observed in BMC or BMD following the 8 weeks. Discussion: Early postoperative MST improved lower extremities maximal muscle strength more than conventional physiotherapy and was accompanied by improvements in postural stability. Conclusion: Implementing MST in early rehabilitation after hip fracture surgery should be considered as a relevant treatment to curtail the downward spiral of reduced ambulatory capacity typical for this patient group, possibly reducing the risk of recuring falls and excess mortality.

• Berg, Ole Kristian; Paulsberg, Fredrik; Brabant, Clara Friederike; Arabsolghar, Keyvan; Ronglan, Sigrid & Bjørnsen, Nina Olinn Åsen [Vis alle 10 forfattere av denne artikkelen] (2020). High-intensity shoulder abduction exercise in subacromial pain syndrome. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 53(1), s. 1–9. doi: 10.1249/MSS.0000000000002436. Vis sammendrag

  Subacromial pain syndrome (SAPS) defined as pain of non-traumatic origin localized around the acromion, is a debilitating, common and often chronic condition. Among many proposed underlying causes of SAPS, hypoperfusion and hypoxic conditions in and around the tendons may be an intrinsic cause of SAPS. Purpose: To determine if adding high intensity aerobic interval training (HIIT) of the rotator cuff to usual care was feasible in SAPS, and improved shoulder endurance more than usual care alone. Additionally, to examine the influence on shoulder pain and disability and the response of tendinous microcirculation following HIIT. Methods: 21 subjects with chronic SAPS were randomized to two groups: Experimental group (EG,n=13) receiving HIIT in addition to treatment as usual, and control group (CG,n=8) receiving treatment as usual. Before and after 8 weeks of exercise therapy, endurance performance was assessed by an incremental abduction exercise of the arm to exhaustion (TTE). Pain and disability was assessed by the shoulder pain and disability index (SPADI). Contrast enhanced ultrasound (CEUS) of the m.supraspinatus and tendon was utilized to indicate tendon blood flow. Results: Endurance in the TTE-test improved by an estimated 233 seconds more on average in EG than in CG (p=0.001, 95%CI:102to363) (p<0.001). The SPADI score was reduced 22 points more on average in EG (p=0.017, 95%CI:-40to-5). The change from pre to post-test was significant in EG for both TTE-test and SPADI improvement (p<0.001). EG also experienced less pain during exercise after the intervention compared to CG (p<0.001). CEUS indicated an increase in tendinous blood flow in EG (p=0.019). Conclusion: HIIT rotator cuff exercise appear to be a feasible intervention in SAPS, increasing endurance performance more than usual care alone.

• Berg, Ole Kristian; Kwon, Oh Sung; Hureau, Thomas J.; Clifton, Heather L.; Thurston, Taylor S. & Le Fur, Yann [Vis alle 11 forfattere av denne artikkelen] (2020). Skeletal muscle mitochondrial adaptations to maximal strength training in older adults. The journals of gerontology. Series A, Biological sciences and medical sciences. ISSN 1079-5006. 75(12), s. 2269–2277. doi: 10.1093/gerona/glaa082. Vis sammendrag

  Maximal Strength Training (MST) results in robust improvements in skeletal muscle force production, efficiency, and mass. However, the effects of MST on muscle mitochondria is still unknown. Accordingly, the purpose of this study was to examine, from the molecular level to whole-muscle, mitochondrial adaptations induced by 8 weeks of knee-extension MST in the quadriceps of 10 older adults using immunoblotting, spectrophotometry, high-resolution respirometry in permeabilized muscle fibers, in vivo31P magnetic resonance spectroscopy (31P-MRS) and gas exchange. As anticipated, MST resulted in an increased isometric knee-extensor force from 133±36 to 147±49 Nm (P<0.05) and quadriceps muscle volume from 1410±103 to 1555±455 cm3 (P<0.05). Mitochondrial complex (I-V) protein abundance and citrate synthase activity were not significantly altered by MST. Assessed ex vivo, maximal ADP-stimulated respiration (state 3CI+CII, PRE: 23±6 and POST: 14±5 ρM·mg-1·s-1, P<0.05), was decreased by MST, predominantly, as a result of a decline in complex I linked respiration (P<0.05). Additionally, state 3 free-fatty acid linked respiration was decreased following MST (PRE: 19±5 and POST: 14±3 ρM·mg-1·s-1, P<0.05). Assessed in vivo, MST slowed the PCr recovery time constant (PRE: 49±13 and POST: 57±16 s, P<0.05) and lowered, by ~20% (P=0.055), the quadriceps peak rate of oxidative ATP synthesis, but did not significantly alter the oxidation of lipid. Although these, likely qualitative, mitochondrial adaptations are potentially negative in terms of skeletal muscle energetic capacity, they need to be considered in light of the many improvements in muscle function that MST affords older adults. Keywords: 31P-MRS, strength training, mitochondrial function

• Berg, Ole Kristian; Kwon, Oh. Sung; Hureau, Thomas J.; Clifton, Heather L.; Thurston, Taylor & Le Fur, Yann [Vis alle 12 forfattere av denne artikkelen] (2018). Maximal strength training increases muscle force generating capacity and the anaerobic ATP synthesis flux without altering the cost of contraction in elderly. Experimental Gerontology. ISSN 0531-5565. 111(October), s. 154–161. doi: 10.1016/j.exger.2018.07.013. Vis sammendrag

  Aging is associated with a progressive decline in skeletal muscle function, then leading to impaired exercise tolerance. Maximal strength training (MST) appears to be a practical and effective intervention to increase both exercise capacity and efficiency. However, the underlying physiological mechanisms responsible for these functional improvements are still unclear. Accordingly, the purpose of this study was to examine the intramuscular and metabolic adaptations induced by 8 weeks of knee-extension MST in the quadriceps of 10 older individuals (75 ± 9 yrs) by employing a combination of molecular, magnetic resonance 1H-imaging and 31P-spectroscopy, muscle biopsies, motor nerve stimulation, and indirect calorimetry techniques. Dynamic and isometric muscle strength were both significantly increased by MST. The greater torque-time integral during sustained isometric maximal contraction post-MST (P = 0.002) was associated with increased rates of ATP synthesis from anaerobic glycolysis (PRE: 10 ± 7 mM·min−1; POST: 14 ± 7 mM·min−1, P = 0.02) and creatine kinase reaction (PRE: 31 ± 10 mM·min−1; POST: 41 ± 10 mM·min−1, P = 0.006) such that the ATP cost of contraction was not significantly altered. Expression of fast myosin heavy chain, quadriceps muscle volume, and submaximal cycling net efficiency were also increased with MST (P = 0.005; P = 0.03 and P = 0.03, respectively). Overall, MST induced a shift toward a more glycolytic muscle phenotype allowing for greater muscle force production during sustained maximal contraction. Consequently, some of the MST-induced improvements in exercise tolerance might stem from a greater anaerobic capacity to generate ATP, while the improvement in exercise efficiency appears to be independent from an alteration in the ATP cost of contraction.

• Nyberg, Stian Kwak; Berg, Ole Kristian; Helgerud, Jan & Wang, Eivind (2018). Reliability of forearm oxygen uptake during handgrip exercise : assessment by ultrasonography and venous blood gas. Physiological Reports. ISSN 2051-817X. 6:e13696(10), s. 1–11. doi: 10.14814/phy2.13696. Fulltekst i vitenarkiv Vis sammendrag

  Assessment of forearm oxygen uptake (O2) during handgrip exercise is a keenly investigated concept for observing small muscle mass metabolism. Although a combination of Doppler ultrasound measurements of brachial artery blood flow () and blood gas drawn from a deep forearm vein has been utilized to calculate forearm O2 for more than two decades, the applicability of this experimental design may benefit from a thorough evaluation of its reliability during graded exercise. Therefore, we evaluated the reliability of this technique during incremental handgrip exercise in ten healthy young (24 ± 3(SD) years.) males. O2 and work rate (WR) exhibited a linear relationship (1.0 W: 43.8 ± 10.1 mL·min−1; 1.5 W: 53.8 ± 14.1 mL·min−1; 2.0 W: 63.4 ± 16.3 mL·min−1; 2.5 W: 72.2 ± 17.6 mL·min−1; 3.0 W: 79.2 ± 18.6 mL·min−1; r = 0.65, P < 0.01). In turn, O2 was strongly associated with (1.0 W: 359 ± 86 mL·min−1; 1.5 W: 431 ± 112 mL·min−1; 2.0 W: 490 ± 123 mL·min−1; 2.5 W: 556 ± 112 mL·min−1; 3.0 W: 622 ± 131 mL·min−1; r = 0.96; P < 0.01), whereas arteriovenous oxygen difference (a‐vO2diff) remained constant following all WRs (123 ± 11–130 ± 10 mL·L−1). Average O2 test–retest difference was −0.4 mL·min−1 with ±2SD limits of agreement (LOA) of 8.4 and −9.2 mL·min−1, respectively, whereas coefficients of variation (CVs) ranged from 4–7%. Accordingly, test–retest difference was 11.9 mL·min−1 (LOA: 84.1 mL·min−1; −60.4 mL·min−1) with CVs between 4 and 7%. Test–retest difference for a‐vO2diff was −0.28 mL·dL−1 (LOA: 1.26mL·dL−1; −1.82 mL·dL−1) with 3–5% CVs. In conclusion, our results revealed that forearm O2 determination by Doppler ultrasound and direct venous sampling is linearly related to WR, and a reliable experimental design across a range of exercise intensities.

• Berg, Ole Kristian; Nyberg, Stian Kwak; Windedal, Tobias Midtvedt & Wang, Eivind (2018). Maximal strength training-induced improvements in forearm work efficiency are associated with reduced blood flow. American Journal of Physiology. Heart and Circulatory Physiology. ISSN 0363-6135. 314(4), s. H853–H862. doi: 10.1152/ajpheart.00435.2017. Fulltekst i vitenarkiv Vis sammendrag

  Maximal strength training (MST) improves work efficiency. However, since blood flow is greatly dictated by muscle contractions in arms during exercise, and vascular conductance is lower, it has been indicated that arms rely more upon adapting oxygen extraction than legs in response to the enhanced work efficiency. Thus, to investigate if metabolic and vascular responses are arm-specific, we utilized Doppler-ultrasound and a catheter placed in the subclavian vein to measure blood flow and a-vO2diff during steady state work in seven young males (24{plus minus}3(SD) years) following six-weeks of handgrip MST. As expected, MST improved maximal strength (49{plus minus}9 to 62{plus minus}10kg) and rate of force development (923{plus minus}224 to 1086{plus minus}238N·s-1), resulting in a reduced submaximal V̇O2 (30{plus minus}9 to 24{plus minus}10ml·min-1) and concomitantly increased work efficiency (9.3{plus minus}2.5 to 12.4{plus minus}3.9%) (all p<0.05). In turn, the work efficiency improvement was associated with a reduced blood flow (486{plus minus}102 to 395{plus minus}114ml·min-1), mediated by a lower blood velocity (43{plus minus}8 to 32{plus minus}6cm·s-1) (all p<0.05). Conduit artery diameter and a-vO2diff remained unaltered. The maximal work test revealed increased time to exhaustion (949{plus minus}239 to 1102{plus minus}292seconds) and maximal work rate (both p<0.05), but no change in peak oxygen uptake. In conclusion, despite prior indications of metabolic and vascular limb-specific differences, these results reveal that improved work efficiency following small muscle mass strength training in the upper extremities is accompanied by a blood flow reduction, and coheres with what has been documented for lower extremities.

• Nyberg, Stian K.; Berg, Ole Kristian; Helgerud, Jan & Wang, Eivind (2017). Blood flow regulation and oxygen uptake during high-intensity forearm exercise. Journal of applied physiology. ISSN 8750-7587. 122(4), s. 907–917. doi: 10.1152/japplphysiol.00983.2016. Vis sammendrag

  The vascular strain is very high during heavy handgrip exercise, but the intensity and kinetics to reach peak blood flow, and peak oxygen uptake, are uncertain. We included 9 young (25 ± 2 yr) healthy males to evaluate blood flow and oxygen uptake responses during continuous dynamic handgrip exercise with increasing intensity. Blood flow was measured using Doppler-ultrasound, and venous blood was drawn from a deep forearm vein to determine arteriovenous oxygen difference (a-vO 2diff) during 6-min bouts of 60, 80, and 100% of maximal work rate (WR max), respectively. Blood flow and oxygen uptake increased ( P < 0.05) from 60%WR max [557 ± 177(SD) ml/min; 56.0 ± 21.6 ml/min] to 80%WR max (679 ± 190 ml/min; 70.6 ± 24.8 ml/min), but no change was seen from 80%WR max to 100%WR max Blood velocity (49.5 ± 11.5 to 58.1 ± 11.6 cm/s) and brachial diameter (0.49 ± 0.05 to 0.50 ± 0.06 cm) showed concomitant increases ( P < 0.05) with blood flow from 60% to 80%WR max, whereas no differences were observed in a-vO 2diff Shear rate also increased ( P < 0.05) from 60% (822 ± 196 s -1) to 80% (951 ± 234 s -1) of WR max The mean response time (MRT) was slower ( P < 0.05) for blood flow (60%WR max 50 ± 22 s; 80%WR max 51 ± 20 s; 100%WR max 51 ± 23 s) than a-vO 2diff (60%WR max 29 ± 9 s; 80%WR max 29 ± 5 s; 100%WR max 20 ± 5 s), but not different from oxygen uptake (60%WR max 44 ± 25 s; 80%WR max 43 ± 14 s; 100%WR max 41 ± 32 s). No differences were observed in MRT for blood flow or oxygen uptake with increased exercise intensity. In conclusion, when approaching maximal intensity, oxygen uptake appeared to reach a critical level at ~80% of WR max and be regulated by blood flow. This implies that high, but not maximal, exercise intensity may be an optimal stimulus for shear stress-induced small muscle mass training adaptations. NEW & NOTEWORTHY This study evaluated blood flow regulation and oxygen uptake during small muscle mass forearm exercise with high to maximal intensity. Despite utilizing only a fraction of cardiac output, blood flow reached a plateau at 80% of maximal work rate and regulated peak oxygen uptake. Furthermore, the results revealed that muscle contractions dictated bulk oxygen delivery and yielded three times higher peak blood flow in the relaxation phase compared with mean values.

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• Berg, Ole Kristian (2024). Det er en virkelighetsfjern svartmaling av sykepleiere med doktorgrad. Sykepleien.no.
• Berg, Ole Kristian (2022). Anatomieksamen 2022: Her er fagnerdene bak årets eksamen. [Tidsskrift]. sykepleien.no.
• Berg, Ole Kristian & Klemetzen, Kristian Havnes (2017). Vit om nærmeste hjertestarter. [Avis]. Romsdals Budstikke. Vis sammendrag

  Treningsfysiolog Ole Kristian Berg med råd til trenere og ledere innenfor idretten. Det er viktig at trenere i det minste har et bevisst forhold til dette med førstehjelp og hjertestarter. Det kan redde liv.

• Wang, Eivind; Nyberg, Stian K.; Berg, Ole Kristian & Helgerud, Jan (2017). Blood flow regulation and oxygen uptake during high intensity forearm exercise. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 49(5S). doi: 10.1249/01.mss.0000519218.77124.86.
• Nyberg, Stian K.; Berg, Ole Kristian; Helgerud, Jan & Wang, Eivind (2017). Validity of forearm oxygen uptake during handgrip exercise : assessment by ultrasonography and venous blood gas. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 49(5S). doi: 10.1249/01.mss.0000517004.27687.52. Vis sammendrag

  Assessment of forearm oxygen uptake (V[Combining Dot Above]O2) during handgrip exercise is a keenly investigated concept for observing small muscle mass metabolism. Although a combination of Doppler-ultrasound measurements of brachial artery blood flow and blood gas drawn from a deep forearm vein has been utilized to calculate forearm V[Combining Dot Above]O2 for more than two decades, this experimental design has, somewhat surprisingly, not been validated.

• Berg, Ole Kristian; Nyberg, Stian K.; Windedal, Tobias M. & Wang, Eivind (2017). Forearm blood flow regulation following maximal strength training-induced improvements in work efficiency. Medicine & Science in Sports & Exercise. ISSN 0195-9131. 49(5S). Vis sammendrag

  Maximal strength training (MST) improves submaximal work efficiency (WE) in the arms. However, since assessment of muscle oxygen uptake (V̇ O2) during exercise is lacking, the behavior of MST-induced adaptations is unknown, and it remains elusive if metabolic and vascular responses in arms may contrast what has been observed in legs.

• Berg, Ole Kristian & Waagbø, Arild Johan (2017). Stipendiat forsker på trening som medisin. [Internett]. Panorama : nettavis for Høgskolen i Molde. Vis sammendrag

  HiMolde-stipendiat Ole Kristian Berg (28) skal undersøke hvordan styrketrening kan hjelpe hoftebruddspasienter. Studien er et ledd i doktorgradsutdanningen i helse- og sosialfag han tar ved HiMolde, og han har satt av 2017 til å undersøke helseeffekten av styrketreningen for 20 hoftebruddspasienter mot en kontrollgruppe på 20 som får ordinær behandling.

• Berg, Ole Kristian & Wang, Eivind (2019). Blood flow regulation and cost of muscle contraction during small muscle mass endurance performance. Høgskolen i Molde - Vitenskapelig høgskole i logistikk.
• Berg, Ole Kristian (2019). Blood flow regulation and cost of muscle contraction during small muscle mass endurance performance. Molde University College - Specialized University in Logistics. ISSN 978-82-7962-243-7.

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