Unless you have really bright continuous lights, it's much better to use flash in portrait photography. You were shooting on ISO 800 or 1600, that is excessive for studio shooting. Your shutter speed was also on 1/60s which does no favors to the sharpness of the image.
Why don't you want to use off camera flash?
I thought someone said earlier it's NOT good to use flash with continuous lights because you have two types of lighting. I dunno...think I'm over this thread.
Constant lights and flash usually have different color temperatures and the issue is known as 'mixed lighting'. Mixed lighting adds some complications to setting the white balance, but strobed light can be gelled to the color temperature of the constant lights as a fairly simple solution to the issue. Gels on the constant lights are prone to melting from the heat constant lights generate, which is why the strobes usually get gelled.
Doing photography well requires understanding both the artistic and technical fundamentals.
Light Science and Magic, Fourth Edition: An Introduction to Photographic Lighting
Photographic Lighting Equipment: A Comprehensive Guide for Digital Photographers
You are having to crank up the ISO and open the lens aperture because continuous lighting isn't as bright to the camera as it is to your eyes.
Lets assume you have a constant light that is 500 watts. That is actually 500 watts in one second, or 500 watts
per second. But you used a shutter speed of 1/60 of a second. So 500 watts divided by 60 = only
8.3 watts that 500 watt light will deliver while the camera shutter is open for just 1/60 of a second. Eight watts is not very much light even for human eyes, let alone being enough light for the camera.
A 500 watt constant light gets really hot, really quickly too.
Strobed light (flash) delivers
a lot more light than constant lights can, but delivers the light in a veery much shorter period of time. A decent hot shoe flash delivers about 75 watt seconds. It is important to note the work
per is not included there. Entry-level studio strobes have power ratings of well over 100 watt seconds. I recommend a minimum of 150 watt seconds for a studio strobe. Studio strobes have low power constant lights (modeling lights) so the photographer can see where the shadows will be when the much brighter strobe fires. In other words, the modeling lights are used as an aid for placing your lights.
A big advantage to using flash is that you can control the ambient light exposure separately from the strobed light exposure with a single shutter release. Shutter speed controls the ambient light exposure, lens aperture controls the strobed light exposure.
The flash of strobed light has a short enough duration the flash of light takes over the motion stopping task of the shutter speed.
Outside or location shooting you will have even less control over the light than you have now shooting in your studio, even using constant lights. Location shooting usually still requires using an array of supplimental lighting gear, like at least a reflector or 2.
Minimalist Lighting: Professional Techniques for Location Photography