TITLE: Isoperimetric inequality for closed curves in $\mathbb{R}^n$
QUESTION [10 upvotes]: A well known isoperimetric inequality for closed curves in $\mathbb{R}^2$ can be generalized to closed curves in $\mathbb{R}^{2n}$, see: https://mathoverflow.net/a/321505/121665.
I have two questions:

Question 1. Is it possible to prove a reasonable isoperimetric inquality for closed curves in $\mathbb{R}^{2n+1}$?
Questions 2. Can an inequality from https://mathoverflow.net/a/321505/121665 be generalized to smooth
  mappings of $\mathbb{S}^k$ to $\mathbb{R}^n$ for some $n>k+1$?

Has anyone seen any related results? 
There is a general isoperimetric inequality for currents (Theorem 6.1 in [1]) that has been generalized in many ways, but I am looking for a more elementary statements, more in the spirit of  https://mathoverflow.net/a/321505/121665.
[1] H. Federer, W. H. Fleming,
Normal and integral currents. 
Ann. of Math.  72 (1960), 458-520.

REPLY [2 votes]: I found one related isoperimetric inequality due to 
Schoenberg [1].
We say that a closed curve in $\mathbb{R}^{2n}$ is convex provided it never crosses a hyperplane more than $2n$ times.

Theorem. Let $C$ be a closed convex curve in $\mathbb{R}^{2n}$ of length $L$. Let $K$ be the convex hull of $C$.
  Then $$ L^{2n}\geq (2\pi n)^n n! (2n)! |K|. $$

Moreover Schoenberg determined all cases of equality.  
The paper of Schoenberg has 12 citations in MathSciNet and some of these papers contain generalizations of Schoenberg's result. In particular Tilli [1] (Corollary 1.3) proved

Theorem. Assume $C\subset\mathbb{R}^n$ is a compact set.  Let $K$ be the convex hull of $C$. Then $$ \mathcal{H}^1(C)^n\geq (n!)^2|K|,
$$ where $\mathcal{H}^1$ stands for the Hausdorff measure.

Clearly the result applies to curves in $\mathbb{R}^n$ of finite length.
See also: Maximizing an integral w.r.t. a measure on the unit sphere.
[1] Schoenberg, I. J.,
An isoperimetric inequality for closed curves convex in even-dimensional Euclidean spaces
.
Acta Math. 91, (1954). 143-164. 
(MathSciNet review).
[2] Tilli, P.,
Isoperimetric inequalities for convex hulls and related questions. .
Trans. Amer. Math. Soc. 362 (2010),  4497-4509. 
(MathSciNet review).