AR-4

The purpose of this study was to examine the effects of active recovery (AR) and passive recovery (PR) using short (2‐min) and long (4‐min) intervals on swimming performance. Twelve male competitive swimmers completed a progressively increasing speed test of 7 × 200‐m swimming repetitions to locate the speed before the onset of curvilinear increase in blood lactate concentration (LT1). Subsequently, performance time of 6 × 50‐m sprints was recorded during four different conditions: (i) 2‐min PR (PR‐2), (ii) 4‐min PR (PR‐4), (iii) 2‐min AR (AR‐2) and (iv) 4‐min AR (AR‐4) intervals. Blood lactate concentration was measured before the first and after the last 50‐m repetition. AR was applied at an intensity corresponding to LT1. Performance as indicated by the time needed to complete 6 × 50‐m sprints was impaired after AR‐4 compared to PR‐4 (AR‐4: 28.65 ± 1.04, PR‐4: 28.17 ± 0.72 s; mean% difference: MD% ±s; ±90% confidence limits: 90%CL, 1.71 ± 3.01%; ±1.43%, p = .01) but was not different between AR‐2 compared to PR‐2 conditions (AR‐2: 28.68 ± 0.85, PR‐2: 28.69 ± 0.82 s; MD%: 0.03 ± 1.61%; 90%CL ± 0.77%, p = .99). Performance in sprint‐6 was improved after AR compared to PR independent of interval duration (AR: 28.55 ± 0.81, PR: 29.01 ± 1.03 s; MD%: 1.52 ± 2.61%; 90%CL ± 1.2%; p = .03). Blood lactate concentration was lower after AR‐4 compared to PR‐4 but did not differ between AR‐2 and PR‐2 conditions. In conclusion, AR impaired performance after a 4‐min but not after a 2‐min interval. A better performance during sprint‐6 after AR could be attributed to a faster metabolic recovery or anticipatory regulatory mechanisms towards the end of the series especially when adequate 4‐min active recovery interval is applied. 

Bone cells (osteoblasts) produce a collagen-rich matrix called osteoid, which is mineralized extracellularly by nanosized calcium phosphate (CaP). Synthetically produced CaP nanoparticles (NPs) have great potential for clinical application. However few studies have compared the effect of CaP NPs with different properties, such as shape and aspect ratio, on the survival and behaviour of active bone-producing cells, such as primary human osteoblasts (HOBs). This study aimed to investigate the biocompatibility and ultrastructural effects of two differently shaped hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ] nanoparticles (HA NPs), round- (aspect ratio 2.12, AR2) and rice-shaped (aspect ratio 3.79, AR4). The ultrastructural response and initial extracellular matrix (ECM) formation of HOBs to HA NPs were observed, as well as matrix vesicle release. A transmission electron microscopy (TEM)-based X-ray microanalytical technique was used to measure cytoplasmic ion levels, including calcium (Ca), phosphorus (P), sodium (Na) and potassium (K). K/Na ratios were used as a measure of cell viability. Following HA NP stimulation, all measured cytoplasmic ion levels increased. AR2 NPs had a greater osteogenic effect on osteoblasts compared with AR4 NPs, including alkaline phosphatase activity and matrix vesicle release. However, they produced only a moderate increase in intracellular Ca and P levels compared with AR4. This suggests that particular Ca and P concentrations may be required for, or indicative of, optimal osteoblast activity. Cell viability, as measured by Na and K microanalysis, was best maintained in AR2. Initial formation of osteoblast ECM was altered in the presence of either HA NP, and immuno-TEM identified fibronectin and matrilin-3 as two ECM proteins affected. Matrilin-3 is here described for the first time as being expressed by cultured osteoblasts. In summary, this novel and in-depth study has demonstrated that HA NP shape can influence a range of different parameters related to osteoblast viability and activity.