Marco Toigo

Six sessions of high-intensity interval training (HIT) are sufficient to improve exercise capacity. The mechanisms explaining such improvements are unclear. Accordingly, the aim of this study was to perform a comprehensive evaluation of physiologically relevant adaptations occurring after six sessions of HIT to determine the mechanisms explaining improvements in exercise performance. Sixteen untrained (43 ± 6 ml·kg(-1)·min(-1)) subjects completed six sessions of repeated (8-12) 60 s intervals of high-intensity cycling (100% peak power output elicited during incremental maximal exercise test) intermixed with 75 s of recovery cycling at a low intensity (30 W) over a 2-wk period. Potential training-induced alterations in skeletal muscle respiratory capacity, mitochondrial content, skeletal muscle oxygenation, cardiac capacity, blood volumes, and peripheral fatigue resistance were all assessed prior to and again following training. Maximal measures of oxygen uptake (Vo2peak; ∼8%; P = 0.026) and cycling time to complete a set amount of work (∼5%; P = 0.008) improved. Skeletal muscle respiratory capacities increased, most likely as a result of an expansion of skeletal muscle mitochondria (∼20%, P = 0.026), as assessed by cytochrome c oxidase activity. Skeletal muscle deoxygenation also increased while maximal cardiac output, total hemoglobin, plasma volume, total blood volume, and relative measures of peripheral fatigue resistance were all unaltered with training. These results suggest that increases in mitochondrial content following six HIT sessions may facilitate improvements in respiratory capacity and oxygen extraction, and ultimately are responsible for the improvements in maximal whole body exercise capacity and endurance performance in previously untrained individuals.

Haemarthrosis triggers haemophilic arthropathy (HA) because bleeding starts synovitis immediately, damages cartilage and leads to loss of function and disability. The aim of our study was to investigate the capacity of ultrasonography (US) in detecting bleeding and joint damage in HA. The joints of 62 patients (pts) with haemophilia A or haemophilia B were consecutively evaluated and scored (score ranging from 0 to 21) for effusion (E), bone remodelling (BR), cartilage damage (CD), synovial hypertrophy (SH), haemosiderin (H), osteophytes (O), haemarthrosis (Hae), erosion (Er) and fibrotic septa (FS) with US. X-rays [Pettersson Score (PXS)] were performed in 61 patients and clinical evaluation [World Federation Haemophiliac orthopaedic score (WFHO)] was performed in all patients. A total of 20 healthy subjects and 20 patients affected by Rheumatoid Arthritis (RA) were used as controls. Power Doppler US (PDUS) was performed in all patients on the knee, ankle and elbow joints. A total of 83 joints were studied (50 knees; 12 elbows and 21 ankles). US showed effusion in 57 joint, bone remodelling in 62, cartilage damage in 64, synovial hypertrophy in 45, haemosiderin in 39, osteophytes in 30, haemarthrosis in 24, erosion in 5 and fibrotic septa in 3. The X-rays score showed remodelling in 47 joints, narrowing joint space in 44, displacement/angulation in 39, osteoporosis in 42, subchondral irregularity in 44, subchondral cyst formation in 37, osteophytes in 36 and erosions in 25. The US score in healthy subjects was always ≤ 5 (range 0 to 4). In haemophiliacs, 34 of 83 joints showed US score ≤ 5, and 49 US score > 5. Joints with US score ≤ 5 had a low PXS (SRCC = 0.375, P < 0.01) and joints with US score > 5 showed a high PXS (SRCC = 0.440, P < 0.01). A significant correlation between US score and PXS for bone remodelling [Spearman's rho Correlation Coefficient (SRCC) = 0.429, P < 0.01] and for osteophytes (SRCC = 0.308, P < 0.05) was found. The correlation between the US score and number of bleedings in 83 joints was very significant (SRCC = 0.375, P < 0.01). A total of 24 bleeding joints were identified and verified with aspiration of haematic fluid. US may detect bone and cartilage alterations and synovitis. Indeed, PDUS identified bleeding also in asymptomatic joints and was able to show different entity of haemarthrosis. US may be a feasible and reliable tool to evaluate joint modifications in HA.

Adequate levels of physical activity are at the center of a healthy lifestyle. However, the molecular mechanisms that mediate the beneficial effects of exercise remain enigmatic. This gap in knowledge is caused by the lack of an amenable experimental model system. Therefore, we optimized electric pulse stimulation of muscle cells to closely recapitulate the plastic changes in gene expression observed in a trained skeletal muscle. The exact experimental conditions were established using the peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha) as a marker for an endurance-trained muscle fiber. We subsequently compared the changes in the relative expression of metabolic and myofibrillar genes in the muscle cell system with those observed in mouse muscle in vivo following either an acute or repeated bouts of treadmill exercise. Importantly, in electrically stimulated C2C12 mouse muscle cells, the qualitative transcriptional adaptations were almost identical to those in trained muscle, but differ from the acute effects of exercise on muscle gene expression. In addition, significant alterations in the expression of myofibrillar proteins indicate that this stimulation could be used to modulate the fiber-type of muscle cells in culture. Our data thus describe an experimental cell culture model for the study of at least some of the transcriptional aspects of skeletal muscle adaptation to physical activity. This system will be useful for the study of the molecular mechanisms that regulate exercise adaptation in muscle.