The anaerobic threshold (AT), the point at which lactic acid starts to accumulates in the muscles, is considered to be somewhere between 85% and 90% of your maximum heart rate (HRmax) .
Ultimately, Windows Defender might fail to update the definitions itself for whatever reason. In such cases you must either force a definition update by navigating to the designated tab of Windows Defender or by downloading and installing the latest signature definitions. The Windows Defender Definition Updates are offline packages containing the most recent antivirus signature for Windows Defender. Once installed, they will make sure your PC is safe from the latest known viruses, spyware, PUPs, and malicious files.
If you think some malware is preventing the installation of Windows Defender definition updates, you may want to run a scan with Microsoft Safety Scanner or for more stubborn malware, using Windows Defender Offline. See how to update Windows 10 offline. These links are sure to interest you too: